Mental calculations

There are 95 NRICH Mathematical resources connected to Mental calculations
I'm Eight
problem

I'm Eight

Age
5 to 11
Challenge level
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Find a great variety of ways of asking questions which make 8.
Roll these Dice
problem

Roll these Dice

Age
7 to 11
Challenge level
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Roll two red dice and a green dice. Add the two numbers on the red dice and take away the number on the green. What are all the different possible answers?
Integrated sums sudoku
page

Integrated sums sudoku

The puzzle can be solved with the help of small clue-numbers which are either placed on the border lines between selected pairs of neighbouring squares of the grid or placed after slash marks on the intersections between two diagonally adjacent squares.
Clever Carl
article

Clever Carl

What would you do if your teacher asked you add all the numbers from 1 to 100? Find out how Carl Gauss responded when he was asked to do just that.
Build it up
problem

Build it up

Age
7 to 11
Challenge level
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Can you find all the ways to get 15 at the top of this triangle of numbers? Many opportunities to work in different ways.