If 5A = 4B, 7B = 3C and 2C = 7D, then A : D is :
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 6 : 5
Each equation gives one ratio, and a chain of ratios is joined by multiplying them, so that B and C cancel.
\(5A=4B\), so \(\displaystyle\frac{A}{B}=\frac{4}{5}\)
\(7B=3C\), so \(\displaystyle\frac{B}{C}=\frac{3}{7}\)
\(2C=7D\), so \(\displaystyle\frac{C}{D}=\frac{7}{2}\)
\(\displaystyle\frac{A}{D}=\frac{A}{B}\times\frac{B}{C}\times\frac{C}{D}=\frac{4}{5}\times\frac{3}{7}\times\frac{7}{2}=\frac{6}{5}\)
So A : D = 6 : 5.