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During a certain week, a seal ate 50 percent of the first 80
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27 May 2019, 15:41
27 May 2019, 15:41
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During a certain week, a seal ate 50 percent of the first 80 smelt it came across, and 30 percent of the remaining smelt it came across. If the seal ate 40 percent of the smelt it came across during the entire week, how many smelt did it eat?
A. 24
B. 32
C. 55
D. 64
E. 80
A. 24
B. 32
C. 55
D. 64
E. 80
GRE Prep Club Tests Editor
Joined: 13 May 2019
Affiliations: Partner at MyGuru LLC.
Posts: 186
Given Kudos: 5
Location: United States
GMAT 1: 770 Q51 V44
GRE 1: Q169 V168
WE:Education (Education)
Re: During a certain week, a seal ate 50 percent of the first 80
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27 May 2019, 16:06
27 May 2019, 16:06
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Expert Reply
Quote:
During a certain week, a seal ate 50 percent of the first 80 smelt it came across, and 30 percent of the remaining smelt it came across. If the seal ate 40 percent of the smelt it came across during the entire week, how many smelt did it eat?
With word problems, first identify the sought value and then work through the problem step-by-step using the most efficient tactic completing obviously necessary calculation as you go and eliminating logically impossible choices along the way.
In this case, the choices correspond to the total number of smelt eaten during a week.
To start the seal ate 50% of the first 80 smelt it encountered. Multiply 80 x 0.5 to determine that so far the seal ate 40 smelt.
Look at the choices knowing that anything < 40 is impossible, so eliminate Choices A and B, 24 and 32 respectively.
Now, consider backsolving starting with the middle remaining choice D to arrive to the correct answer in the most efficient manner, since no matter the outcome, if it's correct, too low or too high, you will logically be able to select the correct answer!
If the seal ate 64 total smelt, that means that 40 were in the first 80, so it ate an additional 64 - 40 = 24 smelt.
According to the problem that 24 smelt, would be 30 percent of the remaining smelt it came across. 24 is 30% of 80 smelt.
Finally, test the 64 smelt it would have eaten out of the theoretical 160 smelt it had encountered to see if 64 is 40% of 160.
64/160 = 40/100, so select Choice D!
Re: During a certain week, a seal ate 50 percent of the first 80
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28 May 2019, 05:55
28 May 2019, 05:55
1
A simpler approach:
Say x is the amount of smelts remainig after the first 80 smelts.
Then 0.5*80 + 0.3x =0.4(80+x) => 8 = 0.1x => x = 80
Total smelt eaten = 0.5*80 + 0.3*80 = 64
Hence (D}
Say x is the amount of smelts remainig after the first 80 smelts.
Then 0.5*80 + 0.3x =0.4(80+x) => 8 = 0.1x => x = 80
Total smelt eaten = 0.5*80 + 0.3*80 = 64
Hence (D}
