Question

Of new calculators tested,8 were defective and 42 passed inspection. What ratio compares the number of defective calculators to the number of new calculators?

Answer 1

You simply put the 2 numbers together to find the answer, which is 8:42.  

You want to find the ratio in its simplest form.  Therefore, you want to find the lowest common multiple of 8 and 42.  
2 goes into both numbers.  
8 / 2 = 4.  
42 / 2 = 21

The answer is 4:21. 

Answer 2

The number of new calculators tested was 50 . . . 8 were bad and 42 were good.

The ratio of defective ones to new ones tested is 8:50 or 4:25 or 16% .