Where one or more of the numbers are 10, or more than 10, and where
there is an _odd_ number of numbers thought of.
Suppose he fixes upon five numbers, viz., 4, 6, 9, 15, 16.
He must add together the numbers as follows, and tell you the various
sums:
1. The sum of the 1st and 2d 10
2. The sum of the 2d and 3d 15
3. The sum of the 3d and 4th 24
4. The sum of the 4th and 5th 31
5. The sum of the 1st and last 20
You must then add together the 1st, 3d, and 5th sums, viz., 10 + 24 +
20 = 54, and the 2d and 4th, 15 + 31 = 46; take one from the other,
leaving 8. The half of this is the first number, 4; if you take this
from the sum of the 1st and 2d you will have the 2d number, 6; this
taken from the sum of the 2d and 3d will give you the 3d, 9; and so on
for the other numbers.