2005 iTest Problems/Problem 28
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Problem
Yoknapatawpha County has 
families. Each family is expected to continue to have children until it has a girl, at which point each family stops having children. If the probability of having a boy is 
, and no families have either fertility problems or multiple children per birthing, how many families are expected to have at least 
children?
Solution 1
The probability of having at least 5 children is the same as having the first 4 children be boys. The probability of 4 boys in a row is 
. To find the expected number of families with at least 5 children, we multiply this probability by the number of families. Thus, our answer is 
.
See Also
| 2005 iTest (Problems, Answer Key) | ||
| Preceded by: Problem 27 |
Followed by: Problem 29 | |
| 1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 • 26 • 27 • 28 • 29 • 30 • 31 • 32 • 33 • 34 • 35 • 36 • 37 • 38 • 39 • 40 • 41 • 42 • 43 • 44 • 45 • 46 • 47 • 48 • 49 • 50 • 51 • 52 • 53 • 54 • 55 • 56 • 57 • 58 • 59 • 60 • TB1 • TB2 • TB3 • TB4 | ||
