20 December

The integers from 2 to 14 (including 2 and 14) are written on 13 cards (one number per card). You and a friend take it in turns to take one of the numbers.
When you have both taken five numbers, you notice that the product of the numbers you have collected is equal to the product of the numbers that your friend has collected. What is the product of the numbers on the three cards that neither of you has taken?

Show answer

15 December

There are 5 ways to make 30 by multiplying positive integers (including the trivial way):
Today's number is the number of ways of making 30030 by multiplying.

Show answer

Not Roman numerals

The letters \(I\), \(V\) and \(X\) each represent a different digit from 1 to 9. If
$$VI\times X=VVV,$$
what are \(I\), \(V\) and \(X\)?

Show answer

Backwards fours

If A, B, C, D and E are all unique digits, what values would work with the following equation?
$$ABCCDE\times 4 = EDCCBA$$

Show answer

10 December

How many zeros does 1000! (ie 1000 × 999 × 998 × ... × 1) end with?

Show answer

17 December

In March, I posted the puzzle One Hundred Factorial, which asked how many zeros 100! ends with.
What is the smallest number, n, such that n! ends with 50 zeros?

One hundred factorial

How many zeros does \(100!\) end with?

Show answer & extension


Show me a random puzzle
 Most recent collections 

Advent calendar 2019

Sunday Afternoon Maths LXVII

Coloured weights
Not Roman numerals

Advent calendar 2018

Sunday Afternoon Maths LXVI

Cryptic crossnumber #2

List of all puzzles


coordinates sums products rugby percentages sum to infinity dominos clocks chalkdust crossnumber dates dodecagons ellipses perfect numbers speed remainders chocolate hexagons the only crossnumber digits multiples graphs logic chess area ave floors algebra sport proportion odd numbers square numbers bases fractions addition angles multiplication spheres arrows pascal's triangle triangle numbers digital clocks volume planes irreducible numbers division star numbers geometry triangles gerrymandering calculus palindromes regular shapes rectangles time cards means cryptic clues factorials median books integers integration sequences probabilty grids christmas folding tube maps dice 2d shapes cryptic crossnumbers polygons differentiation complex numbers coins elections crossnumbers crosswords colouring lines perimeter routes probability range functions symmetry square roots tiling indices balancing mean menace advent wordplay prime numbers shape money unit fractions cube numbers doubling scales people maths averages circles quadratics number squares parabolas games factors taxicab geometry surds crossnumber shapes trigonometry 3d shapes numbers partitions


Show me a random puzzle
▼ show ▼
© Matthew Scroggs 2012–2020