Discussion

A towel when bleached was found to have lost 20% of its length and 10 % of its breadth. The percentage of decrease in the area is:

Answer: A

The area decreases by 28%.

The new length is 80% and the new breadth 90% of the originals, so the new area is

\[ \begin{aligned} 0.80 \times 0.90 &= 0.72 \\ \text{decrease} &= 1 - 0.72 = 0.28 = 28\% \end{aligned} \]

The shortcut for two successive decreases of \(a\%\) and \(b\%\) is \(a + b - \frac{ab}{100} = 20 + 10 - 2 = 28\).

Adding the losses gives 30%, which is not offered; 20% and 10% take one dimension only, and 22% has no basis in the data.

No comment is present. Be the first to comment.

Loading…