GMAT Math : Algebra

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #41 : Algebra

Express the quotient in scientific notation:

\(\displaystyle \left ( 2.4 \times 10 ^{12}\right ) \div \left (6.4 \times 10^{4} \right )\)

Possible Answers:

\(\displaystyle 3.75\times 10 ^ {9 }\)

\(\displaystyle \frac{3}{8} \times 10 ^{8}\)

\(\displaystyle 0.375 \times 10 ^{8}\)

\(\displaystyle \frac{15}{4}\times 10 ^ {7 }\)

\(\displaystyle 3.75\times 10 ^ {7 }\)

Correct answer:

\(\displaystyle 3.75\times 10 ^ {7 }\)

Explanation:

\(\displaystyle \left ( 2.4 \times 10 ^{12}\right ) \div \left (6.4 \times 10^{4} \right )\) 

\(\displaystyle = \frac{ 2.4 \times 10 ^{12} }{6.4 \times 10^{4}}\)

\(\displaystyle = \frac{ 2.4 }{6.4 } \times \frac{ 10 ^{12} }{ 10^{4}}\)

\(\displaystyle =0.375 \times 10 ^{12-4}\)

\(\displaystyle =0.375 \times 10 ^{8}\)

Since 0.375 is not in the range \(\displaystyle \left [1,10 \right )\), we adjust the answer as follows:

\(\displaystyle 0.375 \times 10 ^{8}\)

\(\displaystyle = 3.75\times 10 ^ {-1} \times 10 ^{8}\)

\(\displaystyle = 3.75\times 10 ^ {-1+8 }\)

\(\displaystyle = 3.75\times 10 ^ {7 }\)

Example Question #1123 : Gmat Quantitative Reasoning

Give the result in scientific notation:

\(\displaystyle \left ( 4 \times 10 ^{-7}\right ) ^{3}\)

Possible Answers:

\(\displaystyle 6.4 \times 10 ^{-10}\)

\(\displaystyle 64 \times 10 ^{-4}\)

\(\displaystyle 6.4 \times 10 ^{-22}\)

\(\displaystyle 64 \times 10 ^{-21}\)

\(\displaystyle 6.4 \times 10 ^{-20 }\)

Correct answer:

\(\displaystyle 6.4 \times 10 ^{-20 }\)

Explanation:

\(\displaystyle \left ( 4 \times 10 ^{-7}\right ) ^{3}\)

\(\displaystyle = 4^{3} \times \left ( 10 ^{-7}\right ) ^{3}\)

\(\displaystyle = 64 \times 10 ^{-7\cdot 3}\)

\(\displaystyle = 64 \times 10 ^{-21}\)

Since 64 does not fall in the range \(\displaystyle [1, 10)\), we adjust as follows:

\(\displaystyle 64 \times 10 ^{-21}\)

\(\displaystyle = 6.4\times 10 ^{1} \times 10 ^{-21}\)

\(\displaystyle = 6.4 \times 10 ^{1+ \left (-21 \right )}\)

\(\displaystyle = 6.4 \times 10 ^{-20 }\)

Example Question #13 : Exponents

Give the sum in scientific notation:

\(\displaystyle (8.4 \times 10^{8} ) + (5.7 \times 10 ^{7})\)

Possible Answers:

\(\displaystyle 1.41 \times 10^{16}\)

\(\displaystyle 14.1 \times 10^{15}\)

\(\displaystyle 8.97 \times 10^{8}\)

\(\displaystyle 89.7 \times 10 ^{7}\)

\(\displaystyle 8.97 \times 10^{16}\)

Correct answer:

\(\displaystyle 8.97 \times 10^{8}\)

Explanation:

Rewrite the second addend as follows:

\(\displaystyle (8.4 \times 10^{8} ) + (5.7 \times 10 ^{7})\)

\(\displaystyle =(8.4 \times 10^{8} ) + (0.57 \times 10 ^{1} \times 10 ^{7})\)

\(\displaystyle = (8.4 \times 10^{8} ) + (0.57 \times 10 ^{1+7} )\)

\(\displaystyle = (8.4 \times 10^{8} ) + (0.57 \times 10 ^{8} )\)

\(\displaystyle = (8.4 + 0.57 ) \times 10 ^{8}\)

\(\displaystyle = 8.97 \times 10 ^{8}\)

Example Question #21 : Exponents

Give the sum in scientific notation:

\(\displaystyle (9.63 \times 10^{8} ) + \left ( 8.5 \times 10^{7}\right )\)

Possible Answers:

\(\displaystyle 1.048 \times 10^ {16}\)

\(\displaystyle 17.13 \times 10 ^{15}\)

\(\displaystyle 10.48 \times 10^ {8}\)

\(\displaystyle 1.048 \times 10^ {9}\)

\(\displaystyle 1.713 \times 10 ^{16}\)

Correct answer:

\(\displaystyle 1.048 \times 10^ {9}\)

Explanation:

Rewrite the second addend as follows:

\(\displaystyle (9.63 \times 10^{8} ) + \left ( 8.5 \times 10^{7}\right )\)

\(\displaystyle = (9.63 \times 10^{8} ) + \left ( 0.85 \times 10^ {1} \times 10^{7}\right )\)

\(\displaystyle = (9.63 \times 10^{8} ) + \left ( 0.85 \times 10^ {1+7} \right )\)

\(\displaystyle = (9.63 \times 10^{8} ) + \left ( 0.85 \times 10^ {8} \right )\)

\(\displaystyle = (9.63 + 0.85 ) \times 10^ {8}\)

\(\displaystyle = 10.48 \times 10^ {8}\)

This is not in scientific notation; we adjust as follows:

\(\displaystyle 10.48 \times 10^ {8}\)

\(\displaystyle = 1.048 \times 10^{1} \times 10^ {8}\)

\(\displaystyle = 1.048 \times 10^ {1+ 8}\)

\(\displaystyle = 1.048 \times 10^ {9}\)

Example Question #44 : Algebra

Give the quotient in scientific notation:

\(\displaystyle (1.5 \times 10^{-20}) \div (1.6 \times 10^{-5})\)

Possible Answers:

\(\displaystyle 0.9375 \times 10^{-4}\)

\(\displaystyle 9.375\times 10^{ -5}\)

\(\displaystyle 9.375\times 10^{ -16}\)

\(\displaystyle 0.9375 \times 10^{-15}\)

\(\displaystyle 9.375\times 10^{ -14}\)

Correct answer:

\(\displaystyle 9.375\times 10^{ -16}\)

Explanation:

\(\displaystyle (1.5 \times 10^{-20}) \div (1.6 \times 10^{-5})\)

\(\displaystyle =\frac{ 1.5 \times 10^{-20} }{1.6 \times 10^{- 5}}\)

\(\displaystyle =\frac{ 1.5 }{1.6 } \times \frac{ 10^{-20} }{ 10^{- 5}}\)

\(\displaystyle =0.9375 \times 10^{-20- (-5)}\)

\(\displaystyle =0.9375 \times 10^{-20+5}\)

\(\displaystyle =0.9375 \times 10^{-15}\)

Since 0.9375 does not fall in the range  \(\displaystyle \left [1,10 \right )\), we adjust the answer as follows:

\(\displaystyle 0.9375 \times 10^{-15}\)

\(\displaystyle = 9.375\times 10^{-1} \times 10^{-15}\)

\(\displaystyle = 9.375\times 10^{-1 + (-15)}\)

\(\displaystyle = 9.375\times 10^{ -16}\)

Example Question #21 : Exponents

Give the difference in scientific notation:

\(\displaystyle \left (7 \times 10 ^{9} \right ) - \left (7 \times 10 ^{6} \right )\)

Possible Answers:

\(\displaystyle 7\times 10^{15}\)

\(\displaystyle 1 \times 10^{3}\)

\(\displaystyle 6.93 \times 10 ^{9} \right )\)

\(\displaystyle 6.993 \times 10 ^{9} \right )\)

\(\displaystyle 7\times 10^{3}\)

Correct answer:

\(\displaystyle 6.993 \times 10 ^{9} \right )\)

Explanation:

Rewrite the second addend as follows:

\(\displaystyle \left (7 \times 10 ^{9} \right ) - \left (7 \times 10 ^{6} \right )\)

\(\displaystyle = \left (7 \times 10 ^{9} \right ) - \left (0.007 \times 10 ^{9} \right )\)

\(\displaystyle = \left (7 - 0.007 \right ) \times 10 ^{9} \right )\)

\(\displaystyle =6.993 \times 10 ^{9} \right )\)

Example Question #21 : Understanding Exponents

Express the product in scientific notation:

\(\displaystyle \left ( 8 \times 10 ^{8}\right ) ( 5 \times 10 ^{7})\)

Possible Answers:

\(\displaystyle 4 \times 10 ^{16}\)

\(\displaystyle 40 \times 10 ^{56}\)

\(\displaystyle 4 \times 10 ^{57}\)

\(\displaystyle 40 \times 10 ^{15}\)

\(\displaystyle 0.4 \times 10 ^{58}\)

Correct answer:

\(\displaystyle 4 \times 10 ^{16}\)

Explanation:

\(\displaystyle \left ( 8 \times 10 ^{8}\right ) ( 5 \times 10 ^{7})\)

\(\displaystyle = 8 \times 5 \times 10 ^{8} \times 10 ^{7}\)

\(\displaystyle = 40 \times 10 ^{8+7}\)

\(\displaystyle = 40 \times 10 ^{15 }\)

Since 40 does not fall inside the rangle \(\displaystyle [1,10)\), we adjust the answer as follows:

\(\displaystyle 40 \times 10 ^{15 }\)

\(\displaystyle = 4 \times 10^{1} \times 10 ^{15 }\)

\(\displaystyle = 4 \times 10 ^{1+ 15 }\)

\(\displaystyle = 4 \times 10 ^{16 }\)

Example Question #42 : Algebra

If \(\displaystyle x^2=5\), what does \(\displaystyle x^6\) equal?

Possible Answers:

\(\displaystyle 100\)

\(\displaystyle 15\)

\(\displaystyle 125\)

\(\displaystyle 75\)

\(\displaystyle 25\)

Correct answer:

\(\displaystyle 125\)

Explanation:

We can use the fact that \(\displaystyle (x^a)^b=x^{a*b}\) to see that \(\displaystyle (x^2)^3=x^6.\) 

Since \(\displaystyle x^2=5\), we have

 \(\displaystyle (x^2)^3=(x^2)(x^2)(x^2)=(5)(5)(5)=125\).

Example Question #43 : Algebra

Simplify:

\(\displaystyle \left ( 2x^{2} \right )^{3} \cdot \left ( 2x^{3} \right )^{2}\)

Possible Answers:

\(\displaystyle 32x ^{12}\)

\(\displaystyle 32x ^{10}\)

\(\displaystyle 4,096 x ^{10}\)

\(\displaystyle 24x ^{12}\)

\(\displaystyle 4,096 x ^{12}\)

Correct answer:

\(\displaystyle 32x ^{12}\)

Explanation:

Use the properties of exponents as follows:

\(\displaystyle \left ( 2x^{2} \right )^{3} \cdot \left ( 2x^{3} \right )^{2}\)

\(\displaystyle = 2 ^{3} \cdot \left ( x^{2} \right )^{3} \cdot 2 ^{2} \cdot \left ( x^{3} \right )^{2}\)

\(\displaystyle =8 \cdot x^{2 \; \cdot \; 3} \cdot 4 \cdot x^{3 \; \cdot \; 2}\)

\(\displaystyle =32 \cdot x^{6} \cdot x^{6}\)

\(\displaystyle =32 \cdot x^{6+6}\)

\(\displaystyle =32x^{12}\)

Example Question #44 : Algebra

Solve for \(\displaystyle N\)

\(\displaystyle \left (3 ^{4} \right )^{N}\cdot 3^{5} =\frac{1}{27}\)

Possible Answers:

\(\displaystyle N = \frac{7}{6}\)

\(\displaystyle N = 6\)

The equation has no solution.

\(\displaystyle N= -2\)

\(\displaystyle N = - \frac{3}{20}\)

Correct answer:

\(\displaystyle N= -2\)

Explanation:

\(\displaystyle \left (3 ^{4} \right )^{N}\cdot 3^{5} =\frac{1}{27}\)

\(\displaystyle 3 ^{4\cdot N} \cdot 3^{5} =3 ^{-3 }\)

\(\displaystyle 3 ^{4\cdot N+5} =3 ^{-3 }\)

The left and right sides of the equation have the same base, so we can equate the exponents and solve:

\(\displaystyle 4N + 5 = -3\)

\(\displaystyle 4N + 5 -5 = -3 -5\)

\(\displaystyle 4N = -8\)

\(\displaystyle 4N\div 4 = -8 \div 4\)

\(\displaystyle N= -2\)

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