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On the first even day of the month, Steve Roggers saves $5, and on eac
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17 May 2021, 08:58
17 May 2021, 08:58
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Question Stats:
81% (02:03) correct
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On the first even day of the month, Steve Roggers saves $5, and on each following even day he saves $5 more than he saved the previous even day of the month. If there were 30 days in the certain month, how much money did Steve Roggers save by the end of the month?
A) $680
B) $640
C) $600
D) $580
E) $360
Kudos for the right answer and explanation
Question part of the project GRE Quantitative Reasoning Daily Challenge - (2021) EDITION
GRE - Math Book
A) $680
B) $640
C) $600
D) $580
E) $360
Kudos for the right answer and explanation
Question part of the project GRE Quantitative Reasoning Daily Challenge - (2021) EDITION
GRE - Math Book
Retired Moderator
Joined: 10 Apr 2015
Posts: 6218
Given Kudos: 136
Re: On the first even day of the month, Steve Roggers saves $5, and on eac
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17 May 2021, 09:19
17 May 2021, 09:19
Carcass wrote:
On the first even day of the month, Steve Roggers saves $5, and on each following even day he saves $5 more than he saved the previous even day of the month. If there were 30 days in the certain month, how much money did Steve Roggers save by the end of the month?
A) $680
B) $640
C) $600
D) $580
E) $360
Kudos for the right answer and explanation
Question part of the project GRE Quantitative Reasoning Daily Challenge - (2021) EDITION
GRE - Math Book
A) $680
B) $640
C) $600
D) $580
E) $360
Kudos for the right answer and explanation
Question part of the project GRE Quantitative Reasoning Daily Challenge - (2021) EDITION
GRE - Math Book
Let's use a table to look for a pattern.
Day 2: $5 = 1($5)
Day 4: $5 + $5 = 2($5)
Day 6: $5 + $5 + $5 = 3($5)
Day 8: $5 + $5 + $5 + $5 = 4($5)
.
.
.
Day 28: 14($5)
Day 30: 15($5)
So, TOTAL savings = (1)($5) + (2)($5) + (3)($5) + (4)($5) + . . . . + (14)($5) + (15)($5)
= ($5)(1 + 2 + 3 + 4 + . . . + 14 + 15) [I factored out the $5 from each term]
ASIDE: Here's a useful formula: 1 + 2 + 3 + . . . + n = (n)(n + 1)/2
Now apply this formula to the sum above to get:
= ($5)[(15)(16)/2]
= ($5)(15)(8)
= 600
Answer: C
gmatclubot
Re: On the first even day of the month, Steve Roggers saves $5, and on eac [#permalink]
17 May 2021, 09:19
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