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:
KeikoHHHHTTTT​EphraimHHHTTHTTHHHTTHTT​Same 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