Given:
A box contains four tiles, numbered 1,4,5, and 8. Kelly randomly chooses one tile, places it back in the box, then chooses a second tile.
To find:
The probability that the sum of the two chosen tiles is greater than 7.
Solution:
A box contains four tiles, numbered 1,4,5, and 8. So, the total possible outcomes are:
S = {(1,1),(1,4),(1,5),(1,8),(4,1),(4,4),(4,5),(4,8),(5,1),(5,4),(5,5),(5,8),(8,1),(8,4),(8,5),(8,8)}
n(S) = 16
A : Sum of the two chosen tiles is greater than 7.
A = {(1,8),(4,4),(4,5),(4,8),(5,4),(5,5),(5,8),(8,1),(8,4),(8,5),(8,8)}
n(A) = 11
So, probability that the sum of the two chosen tiles is greater than 7 is


Therefore, the required probability is
.