Question

in a class there are 55% are boys and the girls are 675 whar the no of boys

Answer 1

: 100-55%=45 are girls
45 %of x = 675
45/100x=675
x=675*100/45
1500 are boys

Answer 2

If boys are 55% then girls % is 100% -55%=45% 
 let number of student in class =x
 then 45% of x = 675 
                               or     x ×45\100 =675
                                        x = (675 ×100)÷45
                                         x=1500
then no. of boys = 1500 -675=825.