F.2 Maths Question!!!!!!!!!!!!

Let x L juice from Brand A should be added :
after added :
Brand B:
water: (15% x 2) + (10%)x = 0.3 + 0.1x
Mango juice: (45% x 2) + (20%)x = 0.9 + 0.2x
Pineapple juice: (40% x 2) + (70%)x = 0.8 + 0.7x
such that there is less than 60% of pineapple juice in the mixture :
(100%) * (0.8 + 0.7x) / (0.3 + 0.1x + 0.9 + 0.2x + 0.8 + 0.7x) < 60%
(0.8 + 0.7x) / (2 + x) < 0.6
(8 + 7x) / (2 + x) < 6
8 + 7x < 6(2 + x) , (since 2 + x > 0 , no need to change " < " to " > ")
8 + 7x < 12 + 6x
x < 4
Less than 4L

Q:
Brand A:
Water: 10%
Mango juice: 20%
pineapple juice: 70%

Brand B:
water: 15%
Mango juice: 45%
Pineapple juice: 40%

How much juice from Brand A should be added to the 2L of juice from Brand B, such that there is less than 60% of pineapple juice in the mixture?

A. Let y L of juice from Brand A should be added.
[(70%)y+2(40%)] /(y+2) < 60%
0.7y+0.8 < 0.6*(y+2)
0.7y+0.8 < 0.6y+1.2
0.7y-0.6y < 1.2-0.8
0.1y < 0.4
y < 0.4/0.1
y < 4
Therefore, at most 4L from Brand A should be added to the 2L of juice from Brand B, such that there is less than 60% of pineapple juice in the mixture.

2010-03-25 18:36:42 補充：
Actually, I think percentage of water and mango juice have to be calculated.

2010-03-25 18:49:27 補充：
Correction:
Actually, I think percentage of water and mango juice is not necessary to be calculated.