Question 1110380
Hi there,
28 problems out of 80 correct
28/80 * 100 = 35%  [* means times]
He requires 45%
x/80 * 100 = 45
x/80 = 45/100
x/80 = 0.45
x = 0.45 * 80
x = 36
The boy requires to get at least 36 answers right out of 80
to attain 45% 
Hope this helps :-)