Question 40057
Using logic, I figured the child had to be
1, 2, 3, 4, 5, 6
years of age.
Then I looked at grandma starting at 41 but that didn't work, then 51 but that didn't work, but then I tried 61...
61, 62, 63, 64, 65, 66 works!
The answer is 66.
Good problem.