Mathematical structures

Question

A box contains a number of pens 12 of which are red pens. The rest of the pens in the box are blue pens. If the probability of selecting a red one is 3/8 how many blue pens are in the box?

A) 17

B) 19

C) 20

D) 21

E) 18

Answer 1

12/P = 3/8

cross multiply

3P = 96

divide by 3

P = 96/3 = 32 total Pens

R =12 Red pens

P-R = B

32-12 = 20 Blue pens

C is correct