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Abhi077
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On the first even day of the month, Steve Roggers saves $5 11 Oct 2018, 11:39
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C
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25% (medium)

Question Stats:

80% (02:10) correct 20% (02:54) wrong based on 152 sessions

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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
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C
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BrentGMATPrepNow
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On the first even day of the month, Steve Roggers saves $5 11 Oct 2018, 14:40
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Abhi077
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
Show more

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
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On the first even day of the month, Steve Roggers saves $5 11 Oct 2018, 16:03
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Abhi077
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
Show more

Day 2 = 5
Day 4 = 5 + 5 = 10

This is in the form of 5 + 5(n-1)

Where n is the even day.

30-2 = 28/2 = 14 + 1 = 15 even days.

D30 = 5 + 5(14) = 5 + 70 = 75.

Avg of D2 to D30 = (75+5)/2 = 40 this is possible because it is evenly spaced.

The sum would be = 40*15 = 600

Answer choice C

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On the first even day of the month, Steve Roggers saves $5 Updated on: 17 Oct 2022, 03:32
Originally posted by KarishmaB on 12 Oct 2018, 00:39.
Last edited by KarishmaB on 17 Oct 2022, 03:32, edited 1 time in total.
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Abhi077
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
Show more

You can think about it in terms of an arithmetic progression. There are 15 even days (half of the 30 days) so n = 15
First term of AP (first amount) = $5
Common difference of AP (increase in amount each time) = $5

Sum of all amounts = (n/2)*(2a + (n-1)*d) = (15/2)*(2*5 + (15 - 1)*5) = 600

Answer (C)
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On the first even day of the month, Steve Roggers saves $5 09 Jun 2024, 02:49
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