Question

Katy has a bag of yellow and red balls. There are a total of 30 balls in the bag. The probability of drawing a yellow ball is 1/6. How many red balls should be removed from the bag in order to increase the probability to 1/3?

The answer choices are:
a)5
b)9
c)10
d)12
e)15

Answer 1

The answer is e)15 Because : to find out the possibility of drawin yellow balls we should divide the number of yellow balls to total balls,
Let y be the number of yellow balls:

`\frac { y }{ 30 }` and we know that the possibility is equal to
`\frac { 1 }{ 6 }`

`\frac { y }{ 30 } =\frac { 1 }{ 6 }` from this equation we find y = 5.
If y=5 the number of red balls is 25. If we decrease red balls 15 total number of balls will be = 15. So since number of yellow balls did not change :
`\frac { 5 }{ 15 } =\frac { 1 }{ 3 }`