The average weight of 150 students in the 7th grade is 45 pounds. If the average weight of the boys and girls is 50 pounds and 40 pounds, respectively, then find the number of boys more than the number of girls.

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Solution

Let the number of girls be 'x'.

Number of boys = 150 – x

Total weight of 150 students in the class = 150 $\times$ 45 = 6750

Total weight of 'x' girls = 40x pounds

Total weight of '150 – x' boys =
(150 – x) $\times$ 50 = 7500 – 50x

It is given that the average weight of 150 students is 45.

40x + 7500 – 50x = 6750

10x = 750

x = 75

'x' is the number of girls. So, number of girls = 75

Number of boys = 150 – x = 150 – 75 = 75

Therefore, there are equal number of boys and girls in the class.

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