NEW HERE? LEARN MORE
closeclose
Last visit was: 25 Apr 2024, 02:30 It is currently 25 Apr 2024, 02:30
Decision Tracker
My Rewards
New posts
New comers' posts

Close
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel

On the first even day of the month, Steve Roggers saves $5

SORT BY:
Date
Kudos
Tags:
Find Similar Topics 
Show Tags
Hide Tags
User avatar
L
Abhi077
SC Moderator
Joined: 25 Sep 2018
Posts: 1122
Own Kudos [?]: 2207 [9]
Given Kudos: 1665
Location: United States (CA)
Concentration: Finance, Strategy
Schools: Rotman '21 Jindal '21 Stern '21
GPA: 3.97
WE:Investment Banking (Investment Banking)
Send PM
GMAT ToolKit User Reviews Badge
On the first even day of the month, Steve Roggers saves $5 [#permalink] New post   11 Oct 2018, 11:39
9
Bookmarks
00:00
A
B
C
D
E

Difficulty:

25% (medium)

Question Stats:

81% (02:14) correct 19% (03:12) wrong based on 111 sessions
Hide Show timer Statistics
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
ShowHide Answer
Official Answer
C
Most Helpful Reply
User avatar
L
BrentGMATPrepNow
GMAT Club Legend
GMAT Club Legend
Joined: 12 Sep 2015
Posts: 6821
Own Kudos [?]: 29920 [3]
Given Kudos: 799
Location: Canada
Send PM
Re: On the first even day of the month, Steve Roggers saves $5 [#permalink] New post   11 Oct 2018, 14:40
2
Kudos
1
Bookmarks
Expert Reply
Top Contributor
Abhi077 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


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
General Discussion
User avatar
G
Salsanousi
Senior Manager
Senior Manager
Joined: 19 Oct 2013
Posts: 412
Own Kudos [?]: 306 [2]
Given Kudos: 117
Location: Kuwait
GPA: 3.2
WE:Engineering (Real Estate)
Send PM
GMAT ToolKit User
Re: On the first even day of the month, Steve Roggers saves $5 [#permalink] New post   11 Oct 2018, 16:03
2
Kudos
Abhi077 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


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

Posted from my mobile device
User avatar
L
KarishmaB
Tutor
Joined: 16 Oct 2010
Posts: 14822
Own Kudos [?]: 64907 [2]
Given Kudos: 426
Location: Pune, India
Send PM
On the first even day of the month, Steve Roggers saves $5 [#permalink] New post   Updated on: 17 Oct 2022, 03:32
2
Kudos
Expert Reply
Abhi077 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


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)

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.
GMAT Club Bot
gmatclubot
On the first even day of the month, Steve Roggers saves $5 [#permalink]
12 Oct 2018, 00:39
Moderators:
Bunuel
Math Expert
92912 posts
yashikaaggarwal
Senior Moderator - Masters Forum
3137 posts

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne
Main navigation
GMAT Resources
Partners
MBA Resources
www.gmac.com|www.mba.com | | GMAT Club Rules | Terms and Conditions