In a class of 30 pupils, the ratio of the number of boys to the number of girls is 2:3. How many boys should be added to the class to make an equal numbers of boys and girls?
The total ratio of the number of boys to girls is 2+3 = <<2+3=5>>5
If there are 30 pupils in the class, then each part of the ratio represents 30/5 = <<30/5=6>>6 pupils.
There are currently 6*2 = <<6*2=12>>12 boys in the class.
To have an equal number of boys and girls, 12 boys should be added. Answer: \boxed{12}.