Loading [MathJax]/jax/output/HTML-CSS/jax.js
Home / Aptitude Tests / Mathematics / Some white balls put...

Some white balls put in a basket containing twelve red ba...

Some white balls put in a basket containing twelve red balls and sixteen black balls. If the probability of picking a white balls from the baskets is 3/7, how many white balls were introduced?

A.

12

B.

21

C.

28

D.

32

Correct answer is B

Number of white balls = x
Number of red balls = 12
Number of black balls = 16
Total number of balls = 28 + x
P(white balls) = 3/7
But P(white balls) =x28+x=37=x28+x3(28+x)=7x84+3x=7x7x3x=844x=84x=21