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fozzzy
A certain airline's fleet consisted of 60 type A planes at the beginning of 1980. At the end of each year, starting with 1980, the airline retired 3 of the TYPE A planes and acquired 4 new type B plans. How many years did it take before the number of type A planes left in the airline's fleet was less than 50 percent of the fleet?

A. 6
B. 7
C. 8
D. 9
E. 10

I solved this method using a chart interested in the algebraic approach

60 - 3*n = 4*n , n = 60/7 = 8.5

So, in 8.5 years, there would be equal number of planes A & B(which is of course a hypothetical situation).

So, in 9 years the number of B would be more.

Answer is D.
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Let x = number of years. Each year we lose 3 Type A planes and gain 4 Type B planes.
Since we start off with 60 type A planes and 0 Type B planes, the following equation would determine the point in time where Type A planes = Type B planes
(60-3x) = 4x....this comes to 8 4/7 years. Since we are looking for the number of years (rounded to the nearest whole number) where <50% of the planes are of Type A, this must be > 8 years. So 9 years.
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fozzzy
A certain airline's fleet consisted of 60 type A planes at the beginning of 1980. At the end of each year, starting with 1980, the airline retired 3 of the TYPE A planes and acquired 4 new type B plans. How many years did it take before the number of type A planes left in the airline's fleet was less than 50 percent of the fleet?

A. 6
B. 7
C. 8
D. 9
E. 10

I solved this method using a chart interested in the algebraic approach

Very nice problem fozzy, congrats!
Now this is basically an algebraic translation and that's all we need to do so let's go and nail this

60-3x < 1/2(60+x)

Answer is D

Cheers!
J :)
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I think the best and fastest approach here is to back solve
start with C as usual

No of Years Type A Type B
8 60-8*3= 36 8*4 = 32 --> We need more years
9 60-9*3= 33 9*4 = 36 --> We found answer

Ans: D
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Hi

I actually just plugged in the numbers and got 8. Can someone please clarify?

End of year 1980 -- 57 A and 4 B.
End of year 1981 -- 54 A and 8 B... and so on

End up year 1988 -- 33 A and 36 B

Since that's 8 years, I picked C. It tips over at the end of year 8, so it's still in year 8. Why do we choose 9?
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Hi

I actually just plugged in the numbers and got 8. Can someone please clarify?

End of year 1980 -- 57 A and 4 B.
End of year 1981 -- 54 A and 8 B... and so on

End up year 1988 -- 33 A and 36 B

Since that's 8 years, I picked C. It tips over at the end of year 8, so it's still in year 8. Why do we choose 9?

From the beginning of 1980 to the end of 1988 there are 8 years and 364 days so 9 years.
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So, I also created a table, since for me this was faster and safer than venturing an equation. True, in many cases an equation is the only way to reach an answer in good time, but there is no reason to torture yourself with finding one if you have another option and you cannot readily come up with the correct equation! Right?? :)

______A:60 - 3 per year____B: 0 + 4 per year
Year1______57_______________4
Year2______54_______________8
Year3______51_______________12
Year4______48_______________16
Year5______45_______________20
Year6______42_______________24
Year7______39_______________28
Year8______36_______________32
Year9______33_______________36
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Hi All,

When dealing with questions that can be solved with simple arithmetic and a bit or brute force, it's often best/fastest to just put pen-to-pad and 'map out' the solution. The prompt mentions that planes retired and acquired at the END of each year. You can create a quick table to track what you're looking for:

Start: 60 A and 0 B
Yr 1: 57 A and 4 B
Yr 2: 54 A and 8 B
Yr 3: 51 A and 12 B
Yr 4: 48 A and 16 B
Yr 5: 45 A and 20 B
Yr 6: 42 A and 24 B
Yr 7: 39 A and 28 B
Yr 8: 36 A and 32 B
Yr 9: 33 A and 36 B

After 9 years, the type A planes were less than 50% of the total.

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pacifist85 and Rich demonstrate the utility (and power) of simply creating a table of values.
For more on using tables to solve quantitative questions, watch the following free video - https://www.gmatprepnow.com/module/gmat- ... /video/929

Cheers,
Brent
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Hi

I actually just plugged in the numbers and got 8. Can someone please clarify?

End of year 1980 -- 57 A and 4 B.
End of year 1981 -- 54 A and 8 B... and so on

End up year 1988 -- 33 A and 36 B

Since that's 8 years, I picked C. It tips over at the end of year 8, so it's still in year 8. Why do we choose 9?

From the beginning of 1980 to the end of 1988 there are 8 years and 364 days so 9 years.

Hi Bunuel.

The prompt question asks "How many years did it take BEFORE the number of type A planes". I get confused in choosing between 8 and 9 because of the word "BEFORE". I was wondering if it was a trap and actually took 8 years before the planes A become half of the Fleet.
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Bunuel
russ9
Hi

I actually just plugged in the numbers and got 8. Can someone please clarify?

End of year 1980 -- 57 A and 4 B.
End of year 1981 -- 54 A and 8 B... and so on

End up year 1988 -- 33 A and 36 B

Since that's 8 years, I picked C. It tips over at the end of year 8, so it's still in year 8. Why do we choose 9?

From the beginning of 1980 to the end of 1988 there are 8 years and 364 days so 9 years.

Hi Bunuel.

The prompt question asks "How many years did it take BEFORE the number of type A planes". I get confused in choosing between 8 and 9 because of the word "BEFORE". I was wondering if it was a trap and actually took 8 years before the planes A become half of the Fleet.

"Before" in this context means "until"

How many years did it take until the number of type A planes left in the airline's fleet was less than 50 percent of the fleet?
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The question asks "How many years did it take before the number of type A planes left in the airline's fleet was less than 50 percent of the fleet?"

As many of you pointed out, at x=60/7 i.e. x=8.57, number of A planes = number of B planes.

So at x=9, the number of A is less than the number of B.

But the question asks the number of years before A is less than B? So, shouldn't it be 8? Coz thats the year before A is less than B.
9th year is not the year before A is less than B. It is the year that A is less than B.

Let me know if my interpretation is right.
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Hi jkbk1732,

From what you described, you interpreted the meaning of the question in a quirky way. When dealing with situations in which you're not completely certain about what you're told - or asked for - it can help to think in terms of similar examples from the real world. For example....

How many years old do you have to be BEFORE you are legally allowed to drive a car alone?

When I first received my Driver's License, the required age at that time was 16 years.... so the answer to the above question is 16 (not 15).

In this prompt, we're asked how long it takes to get to a specific outcome (re: the number of type A planes left in the airline's fleet was less than 50 percent of the fleet). Since the change in the number of planes happened at the END of each year, we need 9 years to pass before that outcome is reached.... so the answer is 9 (not 8).

GMAT assassins aren't born, they're made,
Rich
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Not that bad when you set it up as an inequality:

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the best asnwer and the easiest
pacifist85
So, I also created a table, since for me this was faster and safer than venturing an equation. True, in many cases an equation is the only way to reach an answer in good time, but there is no reason to torture yourself with finding one if you have another option and you cannot readily come up with the correct equation! Right?? :)

______A:60 - 3 per year____B: 0 + 4 per year
Year1______57_______________4
Year2______54_______________8
Year3______51_______________12
Year4______48_______________16
Year5______45_______________20
Year6______42_______________24
Year7______39_______________28
Year8______36_______________32
Year9______33_______________36
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