2014 AMC 10B Problem 7

Below is the professionally curated solution for Problem 7 of the 2014 AMC 10B, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2014 AMC 10B solutions, or check the answer key.

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Concepts:percentagealgebraic manipulation

Difficulty rating: 870

7.

Suppose A>B>0A > B > 0 and A is x%x\% greater than B.B. What is x?x?

100(ABB) 100\left(\frac{A-B}{B}\right)

100(A+BB) 100\left(\frac{A+B}{B}\right)

100(A+BA) 100\left(\frac{A+B}{A}\right)

100(ABA) 100\left(\frac{A-B}{A}\right)

100(AB) 100\left(\frac{A}{B}\right)

Solution:

By definition, we know A=x+100100BA = \dfrac {x+ 100}{100}B =B+x100B.= B + \dfrac x{100}B.

This implies, (AB)=x100B100(ABB)=x.\begin{align*} (A-B) &= \dfrac x{100}B\\ 100\left(\dfrac{A-B} B\right) &=x.\end{align*}

Thus, the correct answer is A .

Problem 7 in Other Years