Question

In a shipment of airplane parts, 5% are known to be defective. If 21 parts are found to be defective, how many parts are in the shipment?

Answer 1

We can use ratios and the cross-multiply-divide to find this.

The ratio 21:5 is avaliable via the question. We then need to compare that to the ratio x:100, the 100 being the percent and the x being the number of airplane parts.

21/5 = x/100

We can then solve for x to find the number of airplane parts. First we multiply by 100 on both sides to get 2100/5 = x. Therefore x = 420 and there are 420 airplane parts.