Question

Ryan got $80\%$ of the problems correct on a $25$ -problem test, $90\%$ on a $40$ -problem test, and $70\%$ on a $10$ -problem test. What percent of all the problems did Ryan answer correctly?

$\ 63$

$\ 75$

$\ 80$

$\ 84$

$\ 86$

Answer: D

Concepts:percentage

Difficulty rating: 960

Solution:

There were a total of $25+40+10 = 75$ problems.

On the first test, he solved $0.8\cdot25 = 20$ problems.

On the second test, he solved $0.9\cdot40 = 36$ problems.

On the third test, he solved $0.7\cdot10 = 7$ problems.

Therefore, he solved a total of $20+36+7=63.$ This means the fraction he solved is $\dfrac{63}{75} = 84\%.$

Therefore, the answer is D .

2010 AMC 8 Problem 9

Answer: D

Difficulty rating: 960

Solution:

Problem 9 in Other Years