The ratio of number of girls to number of boy is 2 : 3. If the average weight of the boys is 60 kg and the average weight of both is 51kg, then the average weight of girls is:

45 kg

Given =

The ratio of number of girls to number of boys is 2 : 3

Average weight of the boys is = 60 kg

The average weight of both is = 51kg

Let the average weight of girls is = x

Total average = \(\frac{Total \; weight \; of \; the \; boys + Total \; weight \; of \; girls}{The \; total \; number \; of \; girls \; and \; boys}\)

51 = \(\frac{(60 × 2) + (x × 3)}{2 + 3}\)

51 = \(\frac{(120) + (3x)}{5}\)

255 - 120 = 3x

x = \(\frac{135}{3}\)

x = 45kg