a factory produces 1 defective bulb out of 10 bulbs a yr. if it produces 870 bulbs a yr, how many defective bulbs are produced?  Choices:
A) 84 B) 85 C) 86 D) 87 E) 88

Rationale: 10 out of 1 is defective 20 out of 2 is defective 100 out of 10 is defective and so on 800 out of 80 is defective 70 out of 7 is defective 80 + 7 = 87 answer : d
Answer: D