pzazz12 wrote:
All envelope contains eight bills: 2 ones, 2 fives, 2 tens, and 2 twenties. Two bills are drawn at random without replacement. What is the probability that their sum is $20 or more?
A. 1/4
B. 2/7
C. 3/7
D. 1/2
E. 2/3
The number of ways to select 2 bills from 8 bills is 8C2 =8!/[2!(8-2)!] = (8 x 7)/2! = 28. Now we have to determine the number of ways to select 2 bills that total $20 or more.
If one of the two bills is one of the $20 bills, then the sum is guaranteed to be $20 or more. Thus,
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