Let the common multiple be x . Students in A=3x, Students in B=7x, Students in C=8x. After transferring 10 students from C to B: B becomes 7x+10, and C becomes 8x−10. It is given that B now has 80 students: ⇒7x+10=80 ⇒7x=80−10 ⇒7x=70 ⇒x=10 Students in A=3x=3x10=30 Students in B = 7x=7×10=70 Students in C =8x=8×10=80 Total students =30+70+80=180