AMC 8 L1: Calculation Tricks

Complete problem set with solutions and individual problem pages

Problem 13 Easy

If a@b=\frac{a\times b}{a+b} for a, b positive integers, then what is 5@10? (2010 AMC8 Problem, Question #2)

  • A.

    \frac3{10}

  • B.

    1

  • C.

    2

  • D.

    \frac{10}3

  • E.

    50

Answer:D

Substitude a=5 and b=10 into the expression for a@b to get:

5@10=\frac{5\times10}{5+10}=\frac{50}{15}=\frac{10}{3}.

Thus, answer choice D is correct.

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