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Averages Smart Math

[Smart Math] Averages Problem 2

Here’s and example of a SMART MATH problem for AVERAGES.

Averages

Problem

In a class of 80 students, there are 50 girls and 30 boys. The average weight of the class is 50 lbs. If the average weight of boys is 55 lbs, what is the average weight of girls?

  1. 45 lbs.
  2. 47 lbs.
  3. 53 lbs.
  4. 46 lbs.
  5. 51 lbs.

The Usual Method

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Total weight of class = 80 x 50 = 4000 lbs.

Total weight of boys in the class = 30 x 55 = 1650 lbs.

Total weight of girls in the class = 4000 –1650 = 2350 lbs.

Hence, average weight of girls = \frac{2350}{50} = 47 Lbs.

(Ans: 2)

Estimated Time to arrive at the answer = 45 seconds.

Using Technique

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The difference between 50 lbs and 55 lbs = 5 lbs which is additional per boy in 30 boys. Hence, additional total weight = 30 x 5 = 150 lbs.

This 150 Lbs should be reduced from the weight of girls. Since, there are 50 girls, average reduction per girl will be \frac{150}{50} = 3 lbs.

Hence answer = 50 – 3 = 47 lbs.

(Ans: 2)

Estimated Time to arrive at the answer = 15 seconds.
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