Question

Two single-digit random numbers (0 to 9 inclusive) are selected independently. Find the probability that their sum is 7. (the answer is 2/25, why?)

Answer 1

For the first number:
9 and 8 don't work, so you must pick one of the other 8
=8/10

For the second number:
Again, 9 and 8 don't work. Also, there is only ONE number that will result in a sum of 7
=1/10

1/8 * 1/10= 2/25

Answer 2

MathUser has a small typo

last line should read

\[\frac{8}{10}\times\frac{1}{10}=\frac{8}{100}=\frac{2}{25}\]