We need to find 30% of 20 gallons.
1) We can write a proportion
20 gallons ---- 100%
x gallons --------30%
x = 20*30/100 = 6 gallons
2) Or we can write 30% as decimal.
30% = 30/100 = 0.3
0.3 of 20 = 0.3*20 =6 gallons
Answer 6 gallons are used efficiently.
