The quality control step at the Light Bright Company found that 10 out of every 1000 light bulbs tested is defective. Assuming that this is indicative of all the light bulbs they manufacture, what percent of the manufactured light bulbs works?

%

Find out the number of effective light bulbs first: 1000 – 10 = 990.

Thus, the percent: 990 ÷ 1000 = 0.99 = 99%