AMC8 2010

AMC8 2010 · Q2

AMC8 2010 · Q2. It mainly tests Fractions.

If $a * b = \frac{a \times b}{a+b}$ for $a, b$ positive integers, then what is $5 * 10$?

如果对于正整数$a, b$，定义$a * b = \frac{a \times b}{a+b}$，那么$5 * 10$等于多少？

(A) $\frac{3}{10}$ $\frac{3}{10}$

(B) 1 1

(D) $\frac{10}{3}$ $\frac{10}{3}$

(E) 50 50

Answer

Correct choice: (D)

正确答案：（D）

Solution

Answer (D): $5 * 10 = \frac{5 \times 10}{5+10} = \frac{50}{15} = \frac{5 \times 10}{5 \times 3} = \frac{10}{3}.$

答案（D）：$5 * 10 = \frac{5 \times 10}{5+10} = \frac{50}{15} = \frac{5 \times 10}{5 \times 3} = \frac{10}{3}.$

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