Number of SiblingsProbability puzzles require you to weigh all the possibilities and pick the most likely outcome.
Ten-year-old Bert Sampson lives in the town of Springvale, where, out of all households:
2% include five children
7% include four children
14% include three children
31% include two children
16% include one child
30% do not include any children
What are the chances that Bert lives with two sisters and no brothers?
(Consider all children living in any given house as siblings).
Since Bert is a child, he cannot possibly live in a household with no children. Therefore there is a (14*3)/(16+31*2+14*3+7*4+2*5), or 26.582% chance that he lives with two other children (i.e. in a household with three children).
There is a 50% chance that each of these other children is a girl, so there is a 25% chance that they are both girls.
Therefore, the total chance that Bert lives with two sisters is 25% of 26.582%, or 6.646%.
See another brain teaser just like this one...
Or, just get a random brain teaser
If you become a registered user you can vote on this brain teaser, keep track of
which ones you have seen, and even make your own.
Back to Top