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Percentage Problem
- Thread starter lfd217
- Start date
A substance contains 18% water and 82% oil. How much oil is needed to produce 3600 liters of water.
I know the answer to this problem is: 3600/0.18=20,000 liters, but i've no idea how this makes sense can anyone explain?, thanks.
Let S be the total amount of substance, W be the amount of water in the substance, and O be the amount of oil in the substance. Then
W = 0.18 S
and
O = 0.82 S
Thus when W is 3600, S is given by
S = W / 0.18 = 3600 / 0.18 = 20000
So the amount of substance is 20,000 liters, not the amount of oil. Since the amount of oil is gives as above we have
O = 0.82 S = 0.82 3600 / 0.18 = 16400
Let S be the total amount of substance, W be the amount of water in the substance, and O be the amount of oil in the substance. Then
W = 0.18 S
and
O = 0.82 S
Thus when W is 3600, S is given by
S = W / 0.18 = 3600 / 0.18 = 20000
So the amount of substance is 20,000 liters, not the amount of oil. Since the amount of oil is gives as above we have
O = 0.82 S = 0.82 3600 / 0.18 = 16400
Thanks, what I don't understand though is how come dividing 3600 by the quantity 0.18 gives the total for the whole substance?
Thanks, what I don't understand though is how come dividing 3600 by the quantity 0.18 gives the total for the whole substance?
You know that 18% of the substance is water. If S is the amount of the substance, and W is the amount of water IN that substance, we can write the equation
W = 0.18*S
If we wish to isolate the variable S, we can divide both sides of the equation by 0.18:
W/0.18 = (0.18*S)/0.18
W/0.18 = S
So, to determine the amount of substance (S) it will take to contain the amount of water (W) which is given, we substitute the given amount of water for W: when the amount of water is 3600, we have
3600/0.18 = S