In a class of 100 students, the percentage of boys in the class is

Let boys =b, girls =g and those passed test =t with not passed as n
Since total is 100, % will actually mean the exact number..
So b=t and g=n
Girls passing test =2g/3 or girls not passing=g/3
boys not passing is = g-10
Therefore boys not passing+girls not passing=n=g=g-10+g/3.....g/3=10...g=30
So boys =100-30=70.., thus boys who passed = 70-(30-10)=50
%= 100*50/70=500/7=~70, so 70%

D


Or make a 2*2 matrix

................B................G............total
P................_............2G/3.........B
N............G-10............G/3.........G
T............P...................N...........100
So \(G-10+\frac{G}{3}\)=G.....G=30
Now B+G=100, so B=70
Boys who did not pass =G-10=30-10=20, so boys who passed=70-20=50
% of boys who passed = \(100*\frac{B_p}{B}\)=100*50/70=500/7=(490+10)/7=70+10/7~70%