First put the 20 fifths metres into something a little more recognisable:
20 x 1/5 metres
This is also 20/5 metres
And as 20/5 = 4, 20 fifths metres = 4 metres.
In each metre, there are 100 centimetres,
so 4 metres to 100 centimetres = 4 x 100 = 400 centimetres
So 20 fifths metres is 400 centimetres
