Multiplication and division

problem
Alphabetti Sudoku

Age

11 to 16

Challenge level

This Sudoku requires you to do some working backwards before working forwards.
problem
Producing zeros

Age

11 to 14

Challenge level

Weekly Problem 10 - 2008
If the numbers 1 to 10 are all multiplied together, how many zeros are at the end of the answer?
problem
Pairing up

Age

11 to 14

Challenge level

The numbers 72, 8, 24, 10, 5, 45, 36, 15 are grouped in pairs so that each pair has the same product. Which number is paired with 10?
problem
Mobile numbers

Age

5 to 11

Challenge level

In this investigation, you are challenged to make mobile phone numbers which are easy to remember. What happens if you make a sequence adding 2 each time?
problem
A first product Sudoku

Age

7 to 14

Challenge level

Given the products of adjacent cells, can you complete this Sudoku?
problem
Bus route

Age

11 to 14

Challenge level

How far apart are the first and last bus stops in this bus route?
problem
More mods

Age

14 to 16

Challenge level

What is the units digit for the number 123^(456) ?
problem
Repeaters

Age

11 to 14

Challenge level

Choose any 3 digits and make a 6 digit number by repeating the 3 digits in the same order (e.g. 594594). Explain why whatever digits you choose the number will always be divisible by 7, 11 and 13.
problem
Oh! Hidden inside?

Age

11 to 14

Challenge level

Find the number which has 8 divisors, such that the product of the divisors is 331776.
problem
Factorial

Age

14 to 16

Challenge level

How many zeros are there at the end of the number which is the product of first hundred positive integers?