This question tests 4th grade understanding of addition and subtraction of fractions as joining and separating parts referring to the same whole (CCSS.4.NF.3.a). When fractions have the same denominator, they have the same-sized pieces—the denominator tells us the size (eighths, fourths, thirds, etc.). To add fractions with the same denominator, we join the parts by adding the numerators (the count of pieces) and keeping the denominator the same (the size of pieces). The key understanding: we're adding or subtracting the NUMBER of pieces (numerators), not the SIZE of pieces (denominator). Adding 1/5 and 2/5 means joining 1 fifth with 2 fifths, both parts of the same poster, requiring students to add the numerators and keep the denominator. Choice B is correct because adding the numerators 1 + 2 = 3, keeping denominator 5, giving 3/5, which demonstrates understanding that same-denominator fractions represent same-sized pieces, so we add the count of pieces. Choice A represents adding but changing denominator, which happens when students confuse with equivalent fractions or arithmetic errors. To help students: Use visual models like coloring a poster in fifths to show combining parts. Emphasize denominator stays the same for same size pieces, and use contexts like the same poster.

This question tests 4th grade understanding of addition and subtraction of fractions as joining and separating parts referring to the same whole (CCSS.4.NF.3.a). When fractions have the same denominator, they have the same-sized pieces—the denominator tells us the size (eighths, fourths, thirds, etc.). To subtract fractions with the same denominator, we separate parts by subtracting the numerators and keeping the denominator the same. The key understanding: we're adding or subtracting the NUMBER of pieces (numerators), not the SIZE of pieces (denominator). Subtracting 2/10 from 5/10 means starting with 5 tenths and removing 2 tenths from the same bottle, requiring students to subtract the numerators and keep the denominator. Choice A is correct because subtracting numerators 5 - 2 = 3, keeping denominator 10, giving 3/10, which demonstrates understanding that same-denominator fractions represent same-sized pieces, so we subtract the count of pieces. Choice C represents subtracting numerators but changing to a denominator of 20, which happens when students confuse with finding equivalent fractions or make an arithmetic error. To help students: Use visual models like a water bottle divided into tenths to show subtracting 2/10 from 5/10 leaves 3/10—the size (tenths) stays the same. Emphasize saying it aloud: 'five tenths minus two tenths equals three tenths,' and use concrete contexts like drinking from the same bottle to reinforce same whole.

This question tests 4th grade understanding of addition and subtraction of fractions as joining and separating parts referring to the same whole (CCSS.4.NF.3.a). When fractions have the same denominator, they have the same-sized pieces—the denominator tells us the size (eighths, fourths, thirds, etc.). To subtract fractions with the same denominator, we separate parts by subtracting the numerators and keeping the denominator the same. The key understanding: we're adding or subtracting the NUMBER of pieces (numerators), not the SIZE of pieces (denominator). Subtracting 1/4 from 3/4 means starting with 3 fourths and removing 1 fourth from the same cake, requiring students to subtract the numerators and keep the denominator. Choice A is correct because subtracting numerators 3 - 1 = 2, keeping denominator 4, giving 2/4, which demonstrates understanding that same-denominator fractions represent same-sized pieces, so we subtract the count of pieces. Choice B represents an unrelated fraction, which happens when students change denominators or make calculation errors. To help students: Use fraction bars for cakes to show removing parts—the size (fourths) stays the same. Emphasize subtraction of numerators only, and reinforce same whole with concrete examples.

This question tests 4th grade understanding of addition and subtraction of fractions as joining and separating parts referring to the same whole (CCSS.4.NF.3.a). When fractions have the same denominator, they have the same-sized pieces—the denominator tells us the size (eighths, fourths, thirds, etc.). To add fractions with the same denominator, we join the parts by adding the numerators (the count of pieces) and keeping the denominator the same (the size of pieces). To subtract, we separate parts by subtracting the numerators and keeping the denominator the same. The key understanding: we're adding or subtracting the NUMBER of pieces (numerators), not the SIZE of pieces (denominator). Adding 2/8 and 3/8 means joining 2 eighths with chips and 3 eighths with sprinkles from the same tray, requiring students to add the numerators and keep the denominator. Choice B is correct because adding numerators 2 + 3 = 5, keeping denominator 8, gives 5/8, demonstrating understanding that same-denominator fractions represent same-sized pieces, so we add the count of pieces. Choice A represents multiplying or wrong operation, which happens when students don't perform addition correctly. To help students: Use models like cookie trays to combine groups. Say aloud 'two eighths plus three eighths equals five eighths' to reinforce.

This question tests 4th grade understanding of addition and subtraction of fractions as joining and separating parts referring to the same whole (CCSS.4.NF.3.a). When fractions have the same denominator, they have the same-sized pieces—the denominator tells us the size (eighths, fourths, thirds, etc.). To add fractions with the same denominator, we join the parts by adding the numerators (the count of pieces) and keeping the denominator the same (the size of pieces). The key understanding: we're adding the NUMBER of pieces (numerators), not the SIZE of pieces (denominator). The number line shows jumps of $\frac{1}{10}$, starting at $\frac{3}{10}$ and jumping forward $\frac{4}{10}$ more, requiring students to add the numerators and keep the denominator. Choice C is correct because adding the numerators $3 + 4 = 7$, keeping denominator 10, gives $\frac{7}{10}$, demonstrating understanding that same-denominator fractions represent same-sized pieces, so we add the count of pieces. Choice B represents adding numerators and denominators to get $\frac{12}{10}$, which happens when students think both numerator and denominator change. To help students: Use number lines to show adding $\frac{3}{10} + \frac{4}{10}$ lands at $\frac{7}{10}$—the tenths stay the same size. Emphasize always specifying the same whole and watch for adding denominators; use phrases like 'three tenths plus four tenths equals seven tenths.'

This question tests 4th grade understanding of addition and subtraction of fractions as joining and separating parts referring to the same whole (CCSS.4.NF.3.a). When fractions have the same denominator, they have the same-sized pieces—the denominator tells us the size (eighths, fourths, thirds, etc.). To add fractions with the same denominator, we join the parts by adding the numerators (the count of pieces) and keeping the denominator the same (the size of pieces). To subtract, we separate parts by subtracting the numerators and keeping the denominator the same. The key understanding: we're adding or subtracting the NUMBER of pieces (numerators), not the SIZE of pieces (denominator). Subtracting 1/5 from 4/5 means starting with 4 fifths in the pitcher and removing 1 fifth from the same pitcher, requiring students to subtract the numerators and keep the denominator. Choice B is correct because subtracting numerators 4 - 1 = 3, keeping denominator 5, gives 3/5, demonstrating understanding that same-denominator fractions represent same-sized pieces, so we subtract the count of pieces. Choice A represents a calculation error or different denominator, which happens when students add instead or confuse fractions. To help students: Use models like pitchers to show removing 1/5 from 4/5 leaves 3/5. Emphasize same whole and watch for not recognizing subtraction of pieces.

This question tests 4th grade understanding of addition and subtraction of fractions as joining and separating parts referring to the same whole (CCSS.4.NF.3.a). When fractions have the same denominator, they have the same-sized pieces—the denominator tells us the size (eighths, fourths, thirds, etc.). To subtract fractions with the same denominator, we separate parts by subtracting the numerators and keeping the denominator the same. The key understanding: we're subtracting the NUMBER of pieces (numerators), not the SIZE of pieces (denominator). Subtracting 1/8 from 6/8 means starting with 6 eighths and removing 1 eighth, both parts of the same pitcher. Choice A is correct because subtracting the numerators 6 - 1 = 5, keeping denominator 8, gives 5/8, demonstrating understanding that same-denominator fractions represent same-sized pieces, so we subtract the count of pieces. Choice B represents subtracting denominators or halving, which happens when students don't keep the denominator constant. To help students: Use visual models like pitchers divided into eighths to show removal. Emphasize 'six eighths minus one eighth equals five eighths' and use contexts like drinking from the same pitcher.

This question tests 4th grade understanding of addition and subtraction of fractions as joining and separating parts referring to the same whole (CCSS.4.NF.3.a). When fractions have the same denominator, they have the same-sized pieces—the denominator tells us the size (eighths, fourths, thirds, etc.). To subtract fractions with the same denominator, we separate parts by subtracting the numerators and keeping the denominator the same. The key understanding: we're subtracting the NUMBER of pieces (numerators), not the SIZE of pieces (denominator). Subtracting 2/9 from 7/9 means starting with 7 ninths forward and removing 2 ninths back, both on the same trail. Choice B is correct because subtracting the numerators 7 - 2 = 5, keeping denominator 9, gives 5/9, demonstrating understanding that same-denominator fractions represent same-sized pieces, so we subtract the count of pieces. Choice C represents adding instead of subtracting, which happens when students confuse the direction or operation. To help students: Use number lines to show moving forward and back. Emphasize net distance and use phrases like 'seven ninths minus two ninths equals five ninths from start.'

This question tests 4th grade understanding of addition and subtraction of fractions as joining and separating parts referring to the same whole (CCSS.4.NF.3.a). When fractions have the same denominator, they have the same-sized pieces—the denominator tells us the size (eighths, fourths, thirds, etc.). To add fractions with the same denominator, we join the parts by adding the numerators (the count of pieces) and keeping the denominator the same (the size of pieces). The key understanding: we're adding the NUMBER of pieces (numerators), not the SIZE of pieces (denominator). The question asks why we add numerators of 2/5 and 1/5 while keeping the denominator, focusing on the reason for the rule. Choice A is correct because it explains that fifths are same-sized parts, so we add the number of fifths, demonstrating understanding of why the denominator stays constant. Choice B represents the misconception of adding both numerators and denominators, which happens when students don't understand the denominator represents the size of pieces. To help students: Use visual models to show combining pieces of the same size. Emphasize saying 'two fifths plus one fifth equals three fifths' and watch for common errors like adding denominators.

This question tests 4th grade understanding of addition and subtraction of fractions as joining and separating parts referring to the same whole (CCSS.4.NF.3.a). When fractions have the same denominator, they have the same-sized pieces—the denominator tells us the size (eighths, fourths, thirds, etc.). To add fractions with the same denominator, we join the parts by adding the numerators (the count of pieces) and keeping the denominator the same (the size of pieces). The key understanding: we're adding the NUMBER of pieces (numerators), not the SIZE of pieces (denominator). Adding $\frac{3}{10}$ and $\frac{2}{10}$ means joining 3 tenths with 2 tenths, both parts of the same set of 10 marbles. Choice B is correct because adding the numerators $3 + 2 = 5$, keeping denominator 10, gives $\frac{5}{10}$, demonstrating understanding that same-denominator fractions represent same-sized pieces, so we add the count of pieces. Choice A represents using a different denominator like 100, which happens when students confuse the whole or make arithmetic errors. To help students: Use concrete objects like marbles to show combining groups. Emphasize the same whole and watch for changing denominators incorrectly.