In shop A, if the number of pen drives sold is 120% of the average number of…

Concept

If p% of a quantity is known, divide the known value by p/100 to recover the whole quantity.

A ratio converts one known quantity into the other, an average is the sum divided by the number of terms, and an absolute difference gives the distance between two counts.

Application

1. Since 40% of the cameras sold by shop A is 200, the camera count is 200 ÷ 0.40 = 500.

2. The camera-to-speaker ratio is 5:3, so the speaker count is 500 × 3/5 = 300.

3. Their total with printers is 1160, so the printer count is 1160 − 500 − 300 = 360.

4. The average of the speaker and camera counts is (300 + 500) ÷ 2 = 400. Therefore, the pen-drive count is 120% of 400 = 1.20 × 400 = 480.

5. The required difference is |480 − 360| = 120.

Cross-check

The recovered values satisfy all the shop-A data: 40% of 500 is 200, 500:300 simplifies to 5:3, and 500 + 300 + 360 = 1160.

Result

Therefore, the difference between the numbers of pen drives and printers sold is 120.