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 $=4$