Bunuel wrote:

Official Solution:

If the power of an engine grows by 10% when the number of its cylinders is increased by one, which of the following is closest to the ratio of the power of a 9-cylinder engine to that of a 12-cylinder engine?

A. 0.69

B. 0.71

C. 0.72

D. 0.75

E. 0.78

Let \(X\) denote the power of the 9-cylinder engine and \(Y\) the power of the 12-cylinder engine. It follows from the stem that:

\(Y = 1.1^3 X = 1.21*1.1*X = 1.331X \approx 1\frac{1}{3}X\)

The required ratio is \(\frac{X}{Y} = \frac{1}{1\frac{1}{3}} = \frac{3}{4} = 0.75\)

Answer: D

it is tough to think about such fractions under time pressure.

i was trying to do (10/11)^3 = approx (0.9)^3 but it does not give correct answer