There are 11 tokens in a bag. 6 of them are green 5 of them are red some more red tokens are put into the bag. a token is taken out from the bag at random. the probability that the counter is red is 3/5 How many red tokens where put in the bag ?

1 Answer
Mark D.
Apr 23, 2018

4

Explanation:

If you have 5 red, P(RED)=#5/11#

By adding some red you now change it P(RED)=#3/5#

#3/5=6/10=9/15=12/20# using equivalent fractions. As we had 11 tokens we can ignore the #6/10# fraction but if we look at the #9/15# fraction. The denominator has gone up by 4 and if they were all red then 5+4=9 so there were 4 red tokens added.

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