The picture illustrates the sum 1 + 2 + 3 + 4 = (4 x 5)/2. Prove the general formula for the sum of the first n natural numbers and the formula for the sum of the cubes of the first n natural numbers.
Watch the video to see how Charlie works out the sum. Can you adapt his method?
Here is a machine with four coloured lights. Can you make two lights switch on at once? Three lights? All four lights?