Answer :

Let the number of boys is ‘x' and the number of girls is (150 – x)

Mean weight of 150 students = 60 kg

Mean weight of ‘x’ boys = 70kg

Total weight of boys = 70x

Mean weight of (150 – x) girls = 55

Total weight of girls = (150 – x) × 55

Applying above formula,

70 x – 55 x + 150 × 55 = 150 × 60

15 x + 8250 = 9000

15 x = 750

x = 50

So, the number of boys 50 and number of girls 150 – 50 = 100

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