Problem:
Keiko tosses one penny and Ephraim tosses two pennies. The probability that Ephraim gets the same number of heads that Keiko gets is
Answer Choices:
A. 41
B. 83
C. 21
D. 32
E. 43
Solution:
Make a complete list of equally likely outcomes:
KeikoHHHHTTTTEphraimHHHTTHTTHHHTTHTTSame Number of Heads?NoYesYesNoNoNoNoYes
The probability that they have the same number of heads is 83.
Answer: B.
The problems on this page are the property of the MAA's American Mathematics Competitions