PS1000 Sec5 #19

joyseychow wrote:One-fifth of the light switches produced by a certain factory are defective. Four-fifths of the defective switches are rejected and 1/20 of the nondefective switches are rejected by mistake. If all the switches not rejected are sold, what percent of the switches sold by the factory are
defective?

(A) 4%
(B) 5%
(C) 6.25%
(D) 11%
(E) 16%

Instead of working with fractions I assume that the factory produces 100 units.

From the information above I get
20 units are defective
80 units are good

16 units are defective and rejected
4 units are rejected by mistake
so 20 units are rejected and 80 are sold.

of the 80 that are sold 4 of them are defects that weren't rejected.

4/80 = 5%

B.

very good explanation

Thanks a lot