Factors and multiples

Guess the Dominoes for child and adult. Work out which domino your partner has chosen by asking good questions.

Can you place the nine cards onto a 3x3 grid such that every row, column and diagonal has a product of 1?

Substitution and Transposition all in one! How fiendish can these codes get?

Can you work out what size grid you need to read our secret message?

A student in a maths class was trying to get some information from her teacher. She was given some clues and then the teacher ended by saying, "Well, how old are they?"

How many numbers less than 1000 are NOT divisible by either: a) 2 or 5; or b) 2, 5 or 7?

Weekly Problem 48 - 2013
What is the remainder when the number 743589×301647 is divided by 5?

I am thinking of three sets of numbers less than 101. Can you find all the numbers in each set from these clues?

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.

115^2 = (110 x 120) + 25, that is 13225 895^2 = (890 x 900) + 25, that is 801025 Can you explain what is happening and generalise?