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\(\frac{25b+600}{b+30} = 23\)

Solving, b = 45

Answer: D
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when the average becomes 23 age of girls increase by 3 years and that of boys decreased by 2 years so
3*30=90 and the increasing age of total girls and decreasing age of total boys are equal which is 90 so,
since the average age of boys decreased by 2 years for each: 90/2 becomes the total number of boys.
prove: average = ((45*25)+(30*20))/75)=23
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