Question

10. A drawer contains only green marbles. After

5 red marbles are added to the drawer, the
probability of picking a red marble is
How many marbles were there in the drawer
originally?
(A) 5
(B) 7
(C) 12
(D) 30
(8)

Answer 1

(D) 30

Explanation:

number of green marbles = x

number of red marbles = 5

total number of marbles = x + 5

p(red) = (number of red marbles)/(total number of marbles)

p(red) = 5/(x + 5)

p(red) = 1/7

5/(x + 5) = 1/7

(x + 5) × 1 = 5 × 7

x + 5 = 35

x = 30

Answer: (D) 30