Let the average score of the boys in the mid-semester examination be b.
The average score of the girls is b+5.
In the final exam, the average score of the girls is b+5−3=b+2.
The average score of the entire class increased by 2 and is, therefore, b+2.
\(⇒\frac{20b+30(b+5)}{50}+2\ i.e\ b+5\)
Average score of the boys
\(\frac{50(b+5)-30(b+2)}{20}=b+9.5\)
The increase in the average score of boys is 9.5.