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The ratio of the amount of Alex's fuel oil bill for the month of February to the amount of his fuel oil bill for the month of January was 3/2. If the fuel oil bill for February had been $40 more, the corresponding ratio would have been 5/3. How much was alex's fuel oil bill for January?

a. 240.
b. 300
c. 360
d. 450
e. 540

Please show how you got the answer. Thanks!


A. f/j = 3/2
or f = 3j/2

(f+40)/j = 5/3
or 3f+120 = 5j
or 3 (3j/2) + 120 = 5j
or 9j + 240 = 10j
or f = 240
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ben928
The ratio of the amount of Alex's fuel oil bill for the month of February to the amount of his fuel oil bill for the month of January was 3/2. If the fuel oil bill for February had been $40 more, the corresponding ratio would have been 5/3. How much was alex's fuel oil bill for January?
a. 240.
b. 300
c. 360
d. 450
e. 540

Please show how you got the answer. Thanks!


F/J=3/2
F=3J/2

(F+40)/J=5/3
3F+120=5J
120= 5J-9J/2
J=240
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ben928
The ratio of the amount of Alex's fuel oil bill for the month of February to the amount of his fuel oil bill for the month of January was 3/2. If the fuel oil bill for February had been $40 more, the corresponding ratio would have been 5/3. How much was alex's fuel oil bill for January?
a. 240.
b. 300
c. 360
d. 450
e. 540

Please show how you got the answer. Thanks!


A.

F/J=3/2

F+40/J=5/3

Two equations two unknowns, solving for J leads you to 240.
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ben928
The ratio of the amount of Alex's fuel oil bill for the month of February to the amount of his fuel oil bill for the month of January was 3/2. If the fuel oil bill for February had been $40 more, the corresponding ratio would have been 5/3. How much was alex's fuel oil bill for January?
a. 240.
b. 300
c. 360
d. 450
e. 540

Please show how you got the answer. Thanks!


A.

F/J=3/2

F+40/J=5/3

Two equations two unknowns, solving for J leads you to 240.

I went at it in a different way and got a wrong result.
Can someone see where I went wrong?

2F=3J
3F = 5J-120

6F = 9J
6F = 15J-360

9J = 15J-360

360 = 6J

J = 120.....


anyone?
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ronr34
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ben928
The ratio of the amount of Alex's fuel oil bill for the month of February to the amount of his fuel oil bill for the month of January was 3/2. If the fuel oil bill for February had been $40 more, the corresponding ratio would have been 5/3. How much was alex's fuel oil bill for January?
a. 240.
b. 300
c. 360
d. 450
e. 540

Please show how you got the answer. Thanks!


A.

F/J=3/2

F+40/J=5/3

Two equations two unknowns, solving for J leads you to 240.

I went at it in a different way and got a wrong result.
Can someone see where I went wrong?

2F=3J
3F = 5J-120

6F = 9J
6F = 15J-360

9J = 15J-360

360 = 6J

J = 120.....


anyone?

Should be: 3F = 5J - 120 --> 6F = 10J - 240 (multiplied by 2).

Hope it helps.
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Plug the answers and you will be able to solve it faster.
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Another way to look at this is to calculate the difference that the $40 makes as follows:

5/3j - 3/2j = 40
10/6j - 9/6j = 40
1/6j = 40
j = 240

Thoughts?
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Something is wrong with my method???

3/2 -> Feb is (3/5)x and Jan is (2/5)x

If we add 40 -> (3/5)(x+40) = 5/8x because of the new ratio
3/5x+120/5 = 5/8x
120/5 = 5/8x - 3/5x -> 120/5 = 1/40x
x = 960
2/5(960) = 384????
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immanl
Something is wrong with my method???

3/2 -> Feb is (3/5)x and Jan is (2/5)x

If we add 40 -> (3/5)(x+40) = 5/8x because of the new ratio
3/5x+120/5 = 5/8x
120/5 = 5/8x - 3/5x -> 120/5 = 1/40x
x = 960
2/5(960) = 384????

The issue is the text marked in red above.

For the 2nd scenario, the additional 40 should be added as follows:

(3/5)x + 40 = (5/8) (x+40) ---> x = 600 ....(you multiply x+40 to (5/8)x to account for the fact that x was the total when the original ratio stood. The 'new' total should thus be = old total + 40)

---> Jan = (2/5) *600 = 240. A is the answer.

The way you wrote it above, (3/5)(x+40) means that Feb's contribution is 3/5ths of the total and this equals to 5/8ths as well. This is where you made a mistake.

Hope this helps.
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F=3/2J
3/2J+40=5/3J
40=5/3J-3/2J
40=10/6J-9/6J
40=1/6J
240=J

A. 240.
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ben928
The ratio of the amount of Alex's fuel oil bill for the month of February to the amount of his fuel oil bill for the month of January was 3/2. If the fuel oil bill for February had been $40 more, the corresponding ratio would have been 5/3. How much was Alex's fuel oil bill for January?

A. 240.
B. 300
C. 360
D. 450
E. 540

We are given that the ratio of the amount of Alex's fuel oil bill for the month of February to the amount of his fuel oil bill for the month of January was 3/2. If F = the amount of the Febuary fuel bill and J = the amount of the January fuel bill, we can create the following ratio:

F : J = 3x : 2x

We are also given that if the fuel bill for February had been $40 more, the ratio would have been 5/3. We can create the following equation to determine x:

(3x + 40)/2x = 5/3

3(3x + 40) = 10x

9x + 120 = 10x

120 = x

Thus, the fuel bill in January was 2x = 2(120) = 240 dollars.

Answer: A
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The algebraic solution is straightforward, but we can also test the answers in case one is stuck

Let f = February and j = January
Start by testing B: January = $300
So \(\frac{f}{$300}\) = \(\frac{3}{2}\) ==> f = $450 ==> \(\frac{$450+$40}{300}\) ==> \(\frac{$490}{$300}\), which is slightly less than \(\frac{5}{3}\), so this not our answer. What one can learn from this step is that the answer is close to $300, so you can conveniently eliminate D & E.

Let us try A: January = $240
So \(\frac{f}{$240}\) = \(\frac{3}{2}\) ==> f = $360 ==> \(\frac{$360+$40}{$300}\) ==> \(\frac{$400}{$240}\) = \(\frac{5}{3}\), therefore our answer is A.

The more I practice official questions, the more I get to see how GMAC sets straps for test takers. I know my answer is close to 300, so I have to decide between testing A or C next (notice that they are both $60 from the first answer I tested). I decided to test A only because I already solved the question algebraically.

I need experts' opinions here: which method will you suggest a test taker goes with? Do the algebra or test the answers? Bunuel ScottTargetTestPrep chetan2u EMPOWERgmatRichC VeritasKarishma
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Hi bebs,

TESTing THE ANSWERS works perfectly on this question - and all you had to do was a little Arithmetic to prove what the correct answer was. There is a math 'pattern' that you could save you a little time on this question - and under similar circumstances (especially if you weren't sure whether to TEST Answer A or C next).

Once you determined that Answer B was not a match for what we were looking for (49/30 is clearly less than 50/30 = 5/3, so it's TOO SMALL), we need the extra $40 that's added to February to have a larger 'impact' on the calculation than it did with Answer B. By decreasing the denominator (in this case, going from 300 to 240) we increase the impact that the $40 increase has on the calculation - meaning that the resulting ratio would INCREASE. If you were low on time - and/or you were certain about the pattern - then you could stop working after just TESTing Answer B.

GMAT assassins aren't born, they're made,
Rich
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bebs

I need experts' opinions here: which method will you suggest a test taker goes with? Do the algebra or test the answers? ]

You can test answers, but honestly, you should be able to solve this question without doing so.
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