Question 112635
Notice that the consumption of fuel oil for each of the months is based on the amount used
in September.  So let's identify the unknown consumption in September as "S" gallons.
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The October consumption was 12 gallons more than September. So the October consumption
was S + 12 gallons.
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The November consumption was twice that of September. So the November consumption was 2*S gallons.
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The total consumption for the three months is the sum of these three amounts ... which is:
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S + S + 12 + 2S
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Adding up all the three terms that contain S gallons (that is S + S + 2S) results in 
the total consumption being:
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4S + 12
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But the problem tells you that this total consumption equals 132 gallons. So in equation form
we can write:
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4S + 12 = 132
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Get rid of the 12 on the left side by subtracting 12 from both sides of this equation to get:
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4S = 120
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Solve for S by dividing both sides by 4:
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S = 120/4 = 30 gallons
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If 30 gallons was consumed in September, the October consumption was 12 gallons more,
so it was 42 gallons. And the November consumption was 2 times that of September so
it was 30 times 2 = 60 gallons.
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This means the total consumption was 30 + 42 + 60 and this adds up to 132 gallons,
just as the problem said it should.
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The answer to this problem is:
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September = 30 gallons
October = 42 gallons
November = 60 gallons
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Hope this helps you to understand the problem.
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