There 2 ways to solve this
1- Directly :
80% of water in the fresh berries è 20% of water in the dried berries
36 Ibs of the fresh berries è X Ibs of the dried berries
X = [tex] \frac{36 * 20}{80} [/tex] = 9 Ibs
2- If you do not understand the first method, the second one is more explicit:
First, we gonna calculate the weight of the berries without water (dehydrated):
36 * 80% = 28.8 Ibs (of water in the berries)
Then:
36 – 28.8 = 7.2 Ibs (of completely dehydrated berries)
Next, we gonna add 20% of water in the dehydrated berries:
X (total weight of dried berries) è 100%
7.2 Ibs of dehydrated berries è 80%
X = [tex] \frac{7.2 * 100}{80} [/tex] = 9 Ibs
