So 50 Billion gallons was the residential comsumption for 2010. 1/2 of that is 25 Billion and 35% of that is like 9 billion. Is that the answer?
Households with efficient appliances and good maintenance can reduce water consumption by about 35%. If approximately half of the residential consumption in town W in 2010 was by households with these characteristics, how many billions of gallons of water were saved that year?
Last edited by NDure; 11-19-2011 at 01:07 AM.
Half of the population used efficient appliances.
Half of the population used how much of gallons? => 50/2=25
Now this is the amount they used when they had efficient appliances involved.
Suppose they didnt have those installed, they would have used X gallons
25 IS 35% OF X
saved amount = X - 25 = 38.5 = 25 =~ 14.
I hope this is the answer
65% comes from this: X - .35X=25 Now factor out the X to get: X(1-.35)=25 Now do the subtraction inside the parenthesis: (1-.35)=.65 Therefore X(.65)=25
Now divide 25 by .65: X=25/.65 which equals X=.38.46
38.46 is the amount of water that would have been used by residential if they had not been using efficient appliances and good maintenance. So now the difference between 38.46 and 25 is the amount that was saved.
I'm sorry to necro this thread but this problem is driving me nuts. I understand well and good how the Kaplan book and people in this thread arrived at the answer, but I'm not understanding how it is the correct answer. shridhar22 (and Kaplan) simply take 50% of the total post-efficiency usage and assume that half is the half that was using the efficient appliances. It is not. It is simply half of the total water usage after the reduction has been applied but proportionally has the exact same number of efficient users and inefficient users as the total.
52 billion gallons is arrived by taking 1/2 population using x water per capita and 1/2 population using 0.65x water per capita or:
p = population
x = per capita water usage
(0.5p * x) + (0.5p * 0.65x) = 52 billion gallons
The average water user in this scenario is using 35%/2 less than they would if nobody was using efficient appliances. That means without the efficient users total usage would be 17.5% more than stated, or 61.1 billion gallons for a total savings of 9.1 billion gallons.
Can someone take a look at this? Thank you.
GAD is totally right. 25 is not 35% otherwise it would mean that the two halves just consumed the same amount of water or it is stated that one half are water savers and the other is not so by definition water savers use 35% less water than non water savers.
Saying that X represents the amount of water consumed by the water savers half and Y the amount of water consumed by the non water savers half:
X + Y = 50 and X = Y-35Y/100
Y-35Y/100 + Y = 50
2Y - 35Y/100 = 50
165Y = 5000
Y ~ 30
By deduction X ~ 20 and we saved here 10BG.
However this answer is not listed.
Anyone on this one ?
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