For every set of fifteen batteries, two are said to be defective. out of ninety batteries, how many are not defective?

ANSWER
12 batteries would be defected.
STEP BY STEP.
the ratio is
15:2
For every 15 batteries, 2 are defective
So in order to get from 15 batteries to 90 you multiply
15x6 so
you’d have to multiply 2 as well
2x6
Which in total gives you 12. Defected batteries.

Iwould say they are complementary because that’s the division of a 90 degree angle and it’s split between the middle of them