PSAT Math : How to find a solution to a compound fraction

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #1 : How To Find A Solution To A Compound Fraction

Simplify:

\(\displaystyle \frac{56}{1-\frac{1}{49}}\)

Possible Answers:

\(\displaystyle 54\frac{48}{49}\)

\(\displaystyle 57 \frac{1}{6}\)

\(\displaystyle 55\frac{1}{7}\)

\(\displaystyle 54\frac{6}{7}\)

\(\displaystyle 55\frac{1}{49}\)

Correct answer:

\(\displaystyle 57 \frac{1}{6}\)

Explanation:

\(\displaystyle \frac{56}{1-\frac{1}{49}}\)

\(\displaystyle = 56 \div \left ( 1-\frac{1}{49} \right )\)

\(\displaystyle = 56 \div \left (\frac{49}{49} -\frac{1}{49} \right )\)

\(\displaystyle = \frac{56 }{1}\div \frac{48}{49}\)

\(\displaystyle = \frac{56 }{1}\cdot \frac{49}{48}\)

\(\displaystyle = \frac{7}{1}\cdot \frac{49}{6}\)

\(\displaystyle = \frac{343}{6}\)

\(\displaystyle = 57 \frac{1}{6}\)

Example Question #1 : How To Find A Solution To A Compound Fraction

Simplify:

\(\displaystyle \frac{\frac{3}{4}-\frac{2}{5}}{2- \frac{9}{10}}\)

Possible Answers:

\(\displaystyle \frac{7}{38}\)

\(\displaystyle \frac{77}{200}\)

\(\displaystyle \frac{5}{72}\)

\(\displaystyle \frac{7}{22}\)

\(\displaystyle \frac{147}{200}\)

Correct answer:

\(\displaystyle \frac{7}{22}\)

Explanation:

\(\displaystyle \frac{\frac{3}{4}-\frac{2}{5}}{2- \frac{9}{10}}\)

\(\displaystyle = \left ( \frac{3}{4}-\frac{2}{5} \right ) \div \left ( 2- \frac{9}{10} \right )\)

\(\displaystyle = \left ( \frac{15}{20}-\frac{8}{20} \right ) \div \left ( \frac{20}{10}- \frac{9}{10} \right )\)

\(\displaystyle = \frac{7}{20} \div \frac{11}{10}\)

\(\displaystyle = \frac{7}{20} \cdot \frac{10}{11}\)

\(\displaystyle = \frac{7}{2} \cdot \frac{1}{11}\)

\(\displaystyle = \frac{7}{22}\)

Example Question #3 : How To Find A Solution To A Compound Fraction

Simplify:

\(\displaystyle \frac{1-\frac{1}{4}}{1-\frac{1}{8}}\)

Possible Answers:

\(\displaystyle \frac{21}{32}\)

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

\(\displaystyle \frac{8}{9}\)

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

\(\displaystyle \frac{7}{8}\)

Correct answer:

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

Explanation:

\(\displaystyle \frac{1-\frac{1}{4}}{1-\frac{1}{8}}\)

\(\displaystyle = \left (1 -\frac{1}{4} \right ) \div \left (1-\frac{1}{8} \right )\)

\(\displaystyle = \left (\frac{4}{4}-\frac{1}{4} \right ) \div \left (\frac{8}{8}-\frac{1}{8} \right )\)

\(\displaystyle = \frac{3}{4} \div \frac{7}{8}\)

\(\displaystyle = \frac{3}{4} \cdot \frac{8}{7}\)

\(\displaystyle = \frac{3}{1} \cdot \frac{2}{7}\)

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

Example Question #2 : How To Find A Solution To A Compound Fraction

Simplify:

\(\displaystyle \frac{2-\frac{1}{4}}{1+\frac{1}{7}}\)

Possible Answers:

\(\displaystyle 1\frac{1}{28}\)

None of the other responses gives the correct answer.

\(\displaystyle 1\frac{27}{28}\)

\(\displaystyle 2\)

\(\displaystyle 1 \frac{17}{32}\)

Correct answer:

\(\displaystyle 1 \frac{17}{32}\)

Explanation:

\(\displaystyle \frac{2-\frac{1}{4}}{1+\frac{1}{7}}\)

\(\displaystyle = \left ( 2-\frac{1}{4} \right ) \div \left ( 1+\frac{1}{7} \right )\)

\(\displaystyle = \left (\frac{8}{4}-\frac{1}{4} \right ) \div \left ( \frac{7}{7}+\frac{1}{7} \right )\)

\(\displaystyle = \frac{7}{4} \div \frac{8}{7}\)

\(\displaystyle = \frac{7}{4} \cdot \frac{7}{8}\)

\(\displaystyle = \frac{49}{32}\)

\(\displaystyle = 1 \frac{17}{32}\)

 

Example Question #1 : How To Find A Solution To A Compound Fraction

Simplify:

\(\displaystyle \frac{\frac{1}{3}+\frac{4}{5} }{\frac{2}{3}+\frac{4}{5} }\)

Possible Answers:

\(\displaystyle \frac{2}{9}\)

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

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

\(\displaystyle \frac{17} {22}\)

\(\displaystyle \frac{374}{225}\)

Correct answer:

\(\displaystyle \frac{17} {22}\)

Explanation:

\(\displaystyle \frac{\frac{1}{3}+\frac{4}{5} }{\frac{2}{3}+\frac{4}{5} }\)

\(\displaystyle =\left ( \frac{1}{3}+\frac{4}{5} \right ) \div\left ( \frac{2}{3}+\frac{4}{5} \right )\)

\(\displaystyle =\left ( \frac{5}{15}+\frac{12}{15} \right ) \div\left ( \frac{10}{15}+\frac{12}{15} \right )\)

\(\displaystyle = \frac{17}{15} \div \frac{22}{15}\)

\(\displaystyle = \frac{17}{15} \cdot \frac{15}{22}\)

\(\displaystyle = \frac{17}{1} \cdot \frac{1}{22}\)

\(\displaystyle = \frac{17} {22}\)

Example Question #1 : How To Find A Solution To A Compound Fraction

Simplify:

\(\displaystyle \frac{\frac{1}{2}-\frac{1}{10} }{\frac{1}{4}-\frac{1}{5} }\)

Possible Answers:

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

\(\displaystyle \frac{1}{50}\)

The correct answer is not given among the other responses.

\(\displaystyle 50\)

\(\displaystyle 2\)

Correct answer:

The correct answer is not given among the other responses.

Explanation:

\(\displaystyle \frac{\frac{1}{2}-\frac{1}{10} }{\frac{1}{4}-\frac{1}{5} }\)

\(\displaystyle = \left ( \frac{1}{2}-\frac{1}{10} \right )\div \left ( \frac{1}{4}-\frac{1}{5} \right )\)

\(\displaystyle = \left ( \frac{5}{10}-\frac{1}{10} \right )\div \left ( \frac{5}{20}-\frac{4}{20} \right )\)

\(\displaystyle = \frac{4}{10} \div \frac{1}{20}\)

\(\displaystyle = \frac{4}{10} \cdot \frac{20}{1}\)

\(\displaystyle = \frac{4}{1} \cdot \frac{2}{1}\)

\(\displaystyle = \frac{8}{1} = 8\)

This answer is not among the given choices.

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