GMAT Math : Understanding fractions

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #31 : Understanding Fractions

When positive integer \(\displaystyle n\) is divided by 16, the remainder is 15. What is the remainder when \(\displaystyle n\) is divided by 8 ?

Possible Answers:

\(\displaystyle 3\)

\(\displaystyle 6\)

\(\displaystyle 7\)

\(\displaystyle 5\)

\(\displaystyle 4\)

Correct answer:

\(\displaystyle 7\)

Explanation:

We can set up the following equation from what we are told in the question: \(\displaystyle n = 16q + 15\) where \(\displaystyle q\) is the quotient, then we divide \(\displaystyle n\) by 8: \(\displaystyle \frac{16q+7}{8}\) or \(\displaystyle 2q+\frac{7}{8}\). From there we can  see that \(\displaystyle \frac{7}{8}\) will yield a remainder of \(\displaystyle 7\), which is our final answer.

Example Question #31 : Understanding Fractions

Simplify the following expression: \(\displaystyle \frac{3}{4}-\frac{5}{8}+\frac{3}{16}\)

Possible Answers:

\(\displaystyle \frac{5}{16}\)

\(\displaystyle \frac{3}{2}\)

\(\displaystyle \frac{4}{3}\)

\(\displaystyle \frac{1}{2}\)

\(\displaystyle \frac{5}{8}\)

Correct answer:

\(\displaystyle \frac{5}{16}\)

Explanation:

In order to simplify the expression \(\displaystyle \frac{3}{4}-\frac{5}{8}+\frac{3}{16}\), let's first change the terms to reflect a common denominator:

\(\displaystyle \frac{3\times 4}{4\times 4}-\frac{5\times 2}{8\times 2}+\frac{3}{16}\)

\(\displaystyle =\frac{12}{16}-\frac{10}{16}+\frac{3}{16}\)

\(\displaystyle =\frac{12-10+3}{16}\)

\(\displaystyle =\frac{5}{16}\)

Example Question #33 : Understanding Fractions

When positive integer \(\displaystyle n\) is divided by 12, the remainder is 7. What is the remainder when \(\displaystyle n\) is divided by 3?

Possible Answers:

\(\displaystyle 1\)

\(\displaystyle 3\)

\(\displaystyle 2\)

\(\displaystyle 4\)

\(\displaystyle 5\)

Correct answer:

\(\displaystyle 1\)

Explanation:

The remainder cannot be greater or equal to the divisor, so we can already eliminate 3, 4 and 5. Then, we can set up an equation with the given information. We know that when \(\displaystyle n\) is divided by 12, the remainder is 7 : \(\displaystyle n= 12q + 7\), where \(\displaystyle q\) is the quotient. So, let's try to divide \(\displaystyle n\) by 3 and we get : \(\displaystyle \frac{12q+7}{3}\) or \(\displaystyle 4q + \frac{7}{3}\). Therefore, the remainder must be one, since when 7 is divided by 3, the remainder is \(\displaystyle 1\).

Example Question #1941 : Problem Solving Questions

\(\displaystyle a\) and \(\displaystyle b\) are positive integers and \(\displaystyle \frac{a}{b}= 36.24\). What is the remainder?

Possible Answers:

\(\displaystyle 45\)

\(\displaystyle 22\)

\(\displaystyle 17\)

\(\displaystyle 42\)

\(\displaystyle 34\)

Correct answer:

\(\displaystyle 42\)

Explanation:

We are told that \(\displaystyle \frac{a}{b}=36+0.24\). In other words, the remainder \(\displaystyle r\) can be expressed as follows: 

\(\displaystyle \frac{r}{b}=0.24\) or \(\displaystyle \frac{r}{b}= \frac{24}{100}\)

If we simplify, we get \(\displaystyle \frac{r}{b}= \frac{6}{25}\).

Therefore, we can see that \(\displaystyle r\) is a multiple of \(\displaystyle 6\). The only possible multiple of \(\displaystyle 6\) in the answer choice is \(\displaystyle 42\).

Example Question #32 : Understanding Fractions

What is \(\displaystyle \frac{(5-2)!}{(3-3)!}\) ?

Possible Answers:

\(\displaystyle 6\)

Does not exist 

\(\displaystyle 1\)

\(\displaystyle 2\)

\(\displaystyle 0\)

Correct answer:

\(\displaystyle 6\)

Explanation:

Here we can be tempted to answer that the answer does not exist since there can be no division by 0; however, \(\displaystyle (3-3)!=0!=1\), or in other words, the factorial of 0 is 1. Therefore, the final answer is given by \(\displaystyle 3!\) or \(\displaystyle 6\).

Example Question #31 : Understanding Fractions

\(\displaystyle \frac{3}{8}\) of a number, \(\displaystyle n\), is \(\displaystyle 24\). What is \(\displaystyle n\)?

Possible Answers:

\(\displaystyle 72\)

\(\displaystyle 9\)

\(\displaystyle 8\)

\(\displaystyle 64\)

Correct answer:

\(\displaystyle 64\)

Explanation:

We can solve this problem by setting up our equation and solving for the number, \(\displaystyle n\):

\(\displaystyle \frac{3}{8}n=24\)

\(\displaystyle 3n=(8)(24)\)

\(\displaystyle 3n=192\)

\(\displaystyle n=64\)

Example Question #33 : Understanding Fractions

\(\displaystyle \frac{5}{16}\) of a number, \(\displaystyle n\), is \(\displaystyle 125\). What is the value of \(\displaystyle n\)?

Possible Answers:

\(\displaystyle 39 \frac{1}{6}\)

\(\displaystyle 625\)

\(\displaystyle 400\)

\(\displaystyle 200\)

Correct answer:

\(\displaystyle 400\)

Explanation:

\(\displaystyle \frac{5}{16}n=125\)

\(\displaystyle 5n=(125)(16)\)

\(\displaystyle 5n=2000\)

\(\displaystyle n=400\)

Example Question #33 : Understanding Fractions

Solve: 

\(\displaystyle \frac{3}{8} + \frac{2}{9} =\)

Possible Answers:

\(\displaystyle \frac{43}{72}\)

\(\displaystyle \frac{6}{72}\)

\(\displaystyle \frac{5}{17}\)

\(\displaystyle \frac{5}{9}\)

\(\displaystyle \frac{5}{8}\)

Correct answer:

\(\displaystyle \frac{43}{72}\)

Explanation:

In order to add the two fractions, we must find the lowest common denominator. To do this, we simply multiply  each fraction by the denominator of the opposite over itself:

\(\displaystyle \frac{9}{9}\cdot\frac{3}{8} + \frac{8}{8}\cdot \frac{2}{9} = \frac{27}{72} + \frac{16}{72} = \frac{43}{72}\)

Example Question #1941 : Gmat Quantitative Reasoning

Simplify the following into a single fraction.

 

\(\displaystyle \frac{a}{b} + \frac{6a}{7c}\)

 

 

Possible Answers:

\(\displaystyle \frac{7a}{7c+b}\)

\(\displaystyle \frac{a}{bc}\)

\(\displaystyle \frac{a}{7bc}\)

None of the other answers.

Correct answer:

Explanation:

To simply, we must first find the common denominator of the two fractions. That would be \(\displaystyle b \times 7c\) or \(\displaystyle 7bc\)

Hence we multiply the first fraction by \(\displaystyle \frac{7c}{7c}\) and the second fraction by \(\displaystyle \frac{b}{b}\), and we will have.

 

\(\displaystyle \frac{7ac}{7bc} + \frac{6ab}{7bc}\).

Now that the denominators match, we can add the fractions. The denominator stays the same after this, only the numerators add together.

 

 

Then factor out an \(\displaystyle a\) from the numerator to get the final answer.

 

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