Begin by adding the 2 ratio parts (i.e. the numbers which make up the ratio) so 8+5 = 13.
Then divide the total sum by the sum of the ratio parts. Thus £650/13 = £50.
Multiply this by each of the ratio parts.
£50 * 8 = £400
£50 * 5 = £250
Finish by returning the answers to the correct form. Thus the answer is £400:£250