Solved using overlapping sets:
Total No. of students taking algebra = a
Total No. of students taking geometry = g
Students taking both = 15
So from the information above,
Total No. of students taking only algebra = (a-15)
Total No. of students taking only geometry = (g-15)
Total No of students = (a-15) + (g-15) + 15 = 90;
So, a+g = 105
From the condition given, 2g = a, so substituting
a = 70 & Total No. of students taking only algebra = (a-15) = 55 %
Answer = C
_________________
Kindly press "+1 Kudos" to appreciate