Last year Manfred received 26 paychecks. Each of his first 6 paychecks was $750; each of his remaining paychecks was $30 more than each of his first 6 paychecks. To the nearest dollar, what was the average (arithmetic mean) amount of his paychecks for the year?
(A) $752
(B) $755
(C) $765
(D) $773
(E) $775
OA [spoiler][D][/spoiler]
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- dmateer25
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Here are a couple ways to look at this one.
First 6 are 750 each = 4500
Next 20 are 30 more than the 750. So they are all 780. 780 * 20 = 15600
15600+4500 = 20100 Total paid
20100/26 = ~ 773
Or you can say
6/26 of the payments were 750
6/26 = 3/13 * 750 = 2250/13
20/26 of the payments were 780
20/26 = 10/13 * 780 = 7800/13
(7800 + 2250)/13 = ~ 773
First 6 are 750 each = 4500
Next 20 are 30 more than the 750. So they are all 780. 780 * 20 = 15600
15600+4500 = 20100 Total paid
20100/26 = ~ 773
Or you can say
6/26 of the payments were 750
6/26 = 3/13 * 750 = 2250/13
20/26 of the payments were 780
20/26 = 10/13 * 780 = 7800/13
(7800 + 2250)/13 = ~ 773
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Thanks Dmateer.dmateer25 wrote:Here are a couple ways to look at this one.
First 6 are 750 each = 4500
Next 20 are 30 more than the 750. So they are all 780. 780 * 20 = 15600
15600+4500 = 20100 Total paid
20100/26 = ~ 773
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Great algebraic solutions from dmateer! However, as with many GMAT questions, there are other approaches which may be much quicker.kanha81 wrote:Last year Manfred received 26 paychecks. Each of his first 6 paychecks was $750; each of his remaining paychecks was $30 more than each of his first 6 paychecks. To the nearest dollar, what was the average (arithmetic mean) amount of his paychecks for the year?
(A) $752
(B) $755
(C) $765
(D) $773
(E) $775
If we were in a rush, we could give ourselves a 50/50 shot at this question almost immediately and then use some strategic guessing to answer with no big calculations at all.
In a weighted average, the total average will always be closer to the group with the most weight.
In this question, we have a lot more checks for $780 than for $750. Therefore, the overall average will be weighted toward $780: eliminate (a), (b) and (c).
In fact, in many weighted average questions the answer choice pattern will be:
a) closer to group 1
b) closer to group 1
c) right in the middle
d) closer to group 2
e) closer to group 2
so if you can figure out which group "weighs more" you can often give yourself a quick 50/50 shot (the answer right in the middle is almost always a sucker bet).
Going one step further:
$775 is 25/30 or 5/6 of the way between $750 and $780. For $775 to be correct, the weight of group 2 would have to be 5 times the weight of group 1.
We have 20 checks for $780 and 6 for $750. Is 20:6 = 5:1? Nope, so we can eliminate (e) as well: choose (d).
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Thanks Stuart! Thanks a lot. Until now, I was not aware of the weighted averages. Really an excellent way to narrow down the answer choicesStuart Kovinsky wrote:Great algebraic solutions from dmateer! However, as with many GMAT questions, there are other approaches which may be much quicker.kanha81 wrote:Last year Manfred received 26 paychecks. Each of his first 6 paychecks was $750; each of his remaining paychecks was $30 more than each of his first 6 paychecks. To the nearest dollar, what was the average (arithmetic mean) amount of his paychecks for the year?
(A) $752
(B) $755
(C) $765
(D) $773
(E) $775
If we were in a rush, we could give ourselves a 50/50 shot at this question almost immediately and then use some strategic guessing to answer with no big calculations at all.
In a weighted average, the total average will always be closer to the group with the most weight.
In this question, we have a lot more checks for $780 than for $750. Therefore, the overall average will be weighted toward $780: eliminate (a), (b) and (c).
In fact, in many weighted average questions the answer choice pattern will be:
a) closer to group 1
b) closer to group 1
c) right in the middle
d) closer to group 2
e) closer to group 2
so if you can figure out which group "weighs more" you can often give yourself a quick 50/50 shot (the answer right in the middle is almost always a sucker bet).
Going one step further:
$775 is 25/30 or 5/6 of the way between $750 and $780. For $775 to be correct, the weight of group 2 would have to be 5 times the weight of group 1.
We have 20 checks for $780 and 6 for $750. Is 20:6 = 5:1? Nope, so we can eliminate (e) as well: choose (d).
![Smile :)](./images/smilies/smile.png)
Want to Beat GMAT.
Always do what you're afraid to do. Whoooop GMAT
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His average salary for first six paychecks was $750.For next 20 checks he got $780 in each.He got $30 more in each check.So (30*20)=$600.Now if we divide $ 600 by 26(as there were all together 26 checks) we get an approximate average 23. If we add,then we get 750+23=773.
Hope it helps.
Hope it helps.
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Question - How did you so quickly knew that 775 is 5/6 of the way down from 750 and 780? Thank you!
Stuart Kovinsky wrote:Great algebraic solutions from dmateer! However, as with many GMAT questions, there are other approaches which may be much quicker.kanha81 wrote:Last year Manfred received 26 paychecks. Each of his first 6 paychecks was $750; each of his remaining paychecks was $30 more than each of his first 6 paychecks. To the nearest dollar, what was the average (arithmetic mean) amount of his paychecks for the year?
(A) $752
(B) $755
(C) $765
(D) $773
(E) $775
If we were in a rush, we could give ourselves a 50/50 shot at this question almost immediately and then use some strategic guessing to answer with no big calculations at all.
In a weighted average, the total average will always be closer to the group with the most weight.
In this question, we have a lot more checks for $780 than for $750. Therefore, the overall average will be weighted toward $780: eliminate (a), (b) and (c).
In fact, in many weighted average questions the answer choice pattern will be:
a) closer to group 1
b) closer to group 1
c) right in the middle
d) closer to group 2
e) closer to group 2
so if you can figure out which group "weighs more" you can often give yourself a quick 50/50 shot (the answer right in the middle is almost always a sucker bet).
Going one step further:
$775 is 25/30 or 5/6 of the way between $750 and $780. For $775 to be correct, the weight of group 2 would have to be 5 times the weight of group 1.
We have 20 checks for $780 and 6 for $750. Is 20:6 = 5:1? Nope, so we can eliminate (e) as well: choose (d).
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The value of each paycheck is equal to one of the following:kanha81 wrote:Last year Manfred received 26 paychecks. Each of his first 6 paychecks was $750; each of his remaining paychecks was $30 more than each of his first 6 paychecks. To the nearest dollar, what was the average (arithmetic mean) amount of his paychecks for the year?
(A) $752
(B) $755
(C) $765
(D) $773
(E) $775
OA [spoiler][D][/spoiler]
700+80 or 700+50.
Since $700 is common to all of the paychecks, the average depends only on the LAST TWO DIGITS.
Thus, we can substitute $80 for each $780 paycheck and $50 for each $750 paycheck.
Of the 26 paychecks, there are 20 paychecks for $80 each and 6 paychecks for $50 each.
Average amount per paycheck = (20*80 + 6*50)/26 = 1900/26 = 950/13 ≈ 73.
The correct answer is D.
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Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
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