A box contains 11 marbles, 7 red, and 4 green. Five of these marbles are removed at random. If the probability of drawing a green marble is now 0.5, how many red marbles were removed?

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Answer 1 · 2017-02-18T04:50:04

Then number of red marbles removed were #=4#

Given -

Red marbles #=7#
Green marbles #=4#
Total no of marbles #=11#

Number of Marbles removed #=5#

Marbles in the box #=11-5=6#

Probability of drawing one green marble is #=0.5#

Among the remaining 6 marbles, #x # number of marbles are green.

Then Probability of drawing one green marble is = number of green marbles / Total Number of marbles.

#P_(1 green)=x/6#

We know #P_(1 Green)=0.5#

Then -

#x/6=0.5#
#x=0.5xx 6=3#

After 5 marbles are removed from the box, the number of green marbles remaining is 3.

It means out of 4 green marbles, one green marble has been removed.

Out of 5 marbles one marble is green. Then the other four must be red.

Then number of red marbles removed were #=4#