Given:
total = 750
ratio = 7 : 8
We need to get the ratio of the number to its total
7 + 8 = 15 ; 7/15 and 8/15 is the ratio of the number to its total.
We multiply these ratio to the total of 750
7/15 * 750 = 350
8/15 * 750 = 400
7:8 is equal to 350:400