Subtract your own age from 99. Ask your friend to add this remainder to his age, and then to remove the first figure and add it to the last, telling you the result. This will always be the difference of your ages. Thus, if you are 22, and he is 35, 99 - 22 = 77. Then 35 + 77 = 112. The next process turns this into 13, which, added to your age, gives his age, 35.
No. XXV.—THE HONEYCOMB ILLUSION
In this diagram one hundred and twenty-one circular spots are grouped in a diamond.
If we half close our eyes, and look at this through our eye-lashes, we find that it takes on the appearance of a section of honeycomb, with hexagonal cells.
MULTIPLICATION NO VEXATION
Here is a ready method for multiplying together any two numbers between 12 and 20.
Take one of the two numbers and add it to the unit digit of the other. Beneath the sum thus obtained, but one place to the right, put the product of the unit digits of the two original numbers.
The sum of these new numbers is the product of the numbers that were chosen. Thus:—
| 19 × 13. | (19 + 3) | = | 22 |
| (9 × 3) | = | 27 | |
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