Question 607539
40% fruit juice = x liters


100 * 28% + x * 40% = (100 + x) * 36%
(omit all the % sign)
100 * 28 + x * 40 = (100 + x) * 36
2800 + 40x = 3600 + 36x
40x - 36x = 3600 - 2800
4x = 800
x = 800/4 = 200


so, we should mix 200 liters of 40% fruit juice and the 36% juice mixture will be (100+200) = 300 liters