A complete load of concrete = 8 parts gravel + 7 parts water + 5 parts cement.
Total number of parts in every load = 8 + 7 + 5 = 20 parts
If total load = 220 kg, then 20 parts = 220 kg
Divide each side by 20 : 1 part = 11 kg
gravel = 8 parts = 8 x 11 kg = 88 kg
water = 7 parts = 7 x 11 kg = 77 kg
cement = 5 parts = 5 x 11 kg = 55 kg
Check: 88 + 77 + 55 = 220 yay !