   SEARCH HOME Math Central Quandaries & Queries  Question from Jenny, a teacher: If a + 3b is equal to $175\%$ of 6b, what is the value of a/b? Hi Jenny,

$175\% = \large \frac{175}{100} = \frac{7}{4}$ so "a + 3b is equal to $175\%$ of 6b" can be written

$a + 3b = \frac74\times 6b$

Manipulate this equation until it is in the form

$\mbox{ (a number) } \times a = \mbox{ (a number) } \times b$

from which yo can find the value of $\large \frac{a}{b}.$

I hope this helps. Write back if you need more assistance,
Penny

Jenny wrote back

Thanks Penny for helping me with this problem. It is a question from a middle school math competition. The final answer is 15/2 and I did the exact same work you did, but cannot seem to get that solution.

Hi Jenny,

I multiplied both sides of the equation

$a + 3b = \frac74\times 6b$

by 4 to clear the fraction and got

$4a + 12b = 7 \times 6b = 42b.$

Adding $-12 b$ to each side gives

$4a + 12b -12 b = 42b - 12 b$

so

$4a = 30b.$

Finally multiplying each side by $\large \frac{1}{4b}$ gives

$\frac{1}{4b} \times 4a = \frac{1}{4b} \times 30b.$

or

$\frac{a}{b} = \frac{30}{4} = \frac{15}{2}.$

Penny     Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.