Multiple choice

The average weight of 120 students in the second year class of college is 56 kg. If the average weight of boys and that of girls in the class are 60 kg and 50 kg respectively, then number of boys and girls in the class are respectively :

  1. 72 , 64

  2. 38 , 64

  3. 72, 48

  4. 62 , 58
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using the alligation method: boys average 60, girls 50, overall 56. The difference ratios are (56-50) : (60-56) = 6 : 4 = 3 : 2. Total students 120, so boys = (3/5)*120 = 72 and girls = (2/5)*120 = 48.

AI explanation

Use the alligation method on the averages to find the ratio of boys to girls. The ratio is (56 - 50) to (60 - 56), which is 6 to 4, or 3 to 2. This means out of every 5 students, 3 are boys and 2 are girls. Multiplying these ratio parts by 24 to match the total of 120 students yields 72 boys and 48 girls.

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