Question

If A : B = 3 : 4 and B : C = 5 : 6, then A : C is equal to (A) 1 : 2 (B) 2 : 5 (C) 5 : 8 (D) 7 : 11

Answer 1

L.C.M of b=20.......
A:B=3:4...
B:C=5:6..
making b equal....
A:B=3/4*(5/5)
A:B=15:20..
SIMILARLY....
B:C=5/6*(4/4)
=20:24
A:C=A:B*B:C
A:C=15/24
=5:8....
Hence option c is correct......

Answer 2

In most cases, $A:B=A/B$
Hence, [tex]A/B=3/4 \text{ and } B/C=5/6\\ \text{Multiplying the above eqautions we get,}\\ \frac{A}{B} \times \frac{B}{C} = \frac{3}{4} \times \frac{5}{6} \Rightarrow \frac{A}{C}=\frac{5}{8}\\[/tex]
Hence, $A:B=5:8$
The correct answer is option C.