Puzzles
13 December
A book has 754 pages (numbered 1 to 754: page 1 is on the left of the first double page spread, and page 754 is on the right of the final double page spread). What do the page numbers of the middle two-page spread add up to?
12 December
Put the digits 1 to 9 (using each digit exactly once) in the boxes so that the sums are correct. Today's number is the product of the numbers in the red boxes.
| + | + | = 17 | |||
| + | + | + | |||
| + | + | = 7 | |||
| + | + | + | |||
| + | + | = 21 | |||
| = 11 | = 20 | = 14 |
11 December
Two more than today's number is the reverse of two times today's number.
10 December
How many zeros does 1000! (ie 1000 × 999 × 998 × ... × 1) end with?
9 December
Write the numbers 1 to 15 in a row. Underneath, write the same list without the first and last numbers. Continue this until you have just one number left.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
| 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | ||
| 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | ||||
| etc. | ||||||||||||||
Today's number is the sum of all the numbers you have written.
8 December
The odd numbers are written in a pyramid.
| 1 | ||||
| 3 | 5 | |||
| 7 | 9 | 11 | ||
| etc. | ||||
What is the mean of the numbers in the 23rd row?
7 December
The odd numbers are written in a pyramid.
| 1 | ||||
| 3 | 5 | |||
| 7 | 9 | 11 | ||
| etc. | ||||
What is the sum of the numbers in the seventh row?
4 December
Pick a three digit number whose digits are all different.
Sort the digits into ascending and descending order to form two new numbers. Find the difference between these numbers.
Repeat this process until the number stops changing. The final result is today's number.