Question

a bag contain x red ball and 20 blue balls.the probability of getting red ball is 2/7.find fhe value of x

Answer 1

No. of red balls-x
No. of blue balls-20

Total no. of outcomes=20+x
favorable no. of outcomes=x

$probability \: of \: red \: balls \: = \frac{2}{7} \\ \frac{x}{20 + x} = \frac{2}{7} \\ 7x = 40 + 2x \\ \\ 5x = 40 \\ \\ x = 8$
there are 8 red balls!!

Answer 2

Total number of balls = 20 + x

x / (20 + x) = 2/7

7x = 40 + 2x

5x = 40

x = 8 ⇒there are 8 red balls.