NEW HERE? LEARN MORE
closeclose
Last visit was: 24 Apr 2024, 21:20 It is currently 24 Apr 2024, 21:20
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

Chu-Li has $100 in her piggy bank. How much will she have in her bank

SORT BY:
Date
Kudos
Tags:
Find Similar Topics 
Show Tags
Hide Tags
User avatar
L
Bunuel
Math Expert
Joined: 02 Sep 2009
Posts: 92900
Own Kudos [?]: 618840 [30]
Given Kudos: 81588
Send PM
CAT Tests Forum Quiz Mode
Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   17 Aug 2018, 12:26
1
Kudos
29
Bookmarks
Expert Reply
00:00
A
B
C
D
E

Difficulty:

15% (low)

Question Stats:

78% (01:34) correct 22% (01:53) wrong based on 542 sessions
Hide Show timer Statistics
Chu-Li has $100 in her piggy bank. How much will she have in her bank 40 weeks from now if she puts $1 in the bank next week, $2 two weeks from now, $3 three weeks from now, and continues to increase the amount that she puts in by $1 each week?

A. $140
B. $800
C. $920
D. $1640
E. $1740
ShowHide Answer
Official Answer
C
Most Helpful Reply
User avatar
P
JeffTargetTestPrep
Target Test Prep Representative
Joined: 04 Mar 2011
Status:Head GMAT Instructor
Affiliations: Target Test Prep
Posts: 3043
Own Kudos [?]: 6272 [9]
Given Kudos: 1646
Send PM
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   20 Aug 2018, 11:05
6
Kudos
3
Bookmarks
Expert Reply
Bunuel wrote:
Chu-Li has $100 in her piggy bank. How much will she have in her bank 40 weeks from now if she puts $1 in the bank next week, $2 two weeks from now, $3 three weeks from now, and continues to increase the amount that she puts in by $1 each week?

A. $140
B. $800
C. $920
D. $1640
E. $1740


Since sum = average x quantity and we have a set of evenly spaced numbers:

The average of an evenly spaced set of numbers is (smallest + greatest)/2, so average = (1 + 40)/2 = 41/2

sum = 41/2 x 40 = 41 x 20 = 820

Since she started with 100 dollars, she will have 920 dollars after 40 weeks.

Answer: C
General Discussion
User avatar
G
CounterSniper
Director
Director
Joined: 20 Feb 2015
Posts: 631
Own Kudos [?]: 712 [3]
Given Kudos: 74
Concentration: Strategy, General Management
Send PM
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   17 Aug 2018, 12:41
1
Kudos
2
Bookmarks
Bunuel wrote:
Chu-Li has $100 in her piggy bank. How much will she have in her bank 40 weeks from now if she puts $1 in the bank next week, $2 two weeks from now, $3 three weeks from now, and continues to increase the amount that she puts in by $1 each week?

A. $140
B. $800
C. $920
D. $1640
E. $1740



100 + sum of 1st 40 terms
100 + 40(41)/2
100 + 820
920
C
User avatar
D
PKN
Director
Director
Joined: 01 Oct 2017
Status:Learning stage
Posts: 827
Own Kudos [?]: 1298 [0]
Given Kudos: 41
WE:Supply Chain Management (Energy and Utilities)
Send PM
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   17 Aug 2018, 12:42
Bunuel wrote:
Chu-Li has $100 in her piggy bank. How much will she have in her bank 40 weeks from now if she puts $1 in the bank next week, $2 two weeks from now, $3 three weeks from now, and continues to increase the amount that she puts in by $1 each week?

A. $140
B. $800
C. $920
D. $1640
E. $1740


Cumulative amount of money in 40 weeks: 1+2+3+...............+40=\(\frac{40*41}{2}\)=820

Total savings=Base deposit+Additional deposit in 40 weeks=100+820=$920

Ans. (C)
avatar
B
vdsmba
Intern
Intern
Joined: 03 Sep 2017
Posts: 43
Own Kudos [?]: 8 [0]
Given Kudos: 57
Location: India
Schools: Anderson '22 (M) Darden '22 (D) Kellogg '22 (WL) Ross '22 (D) ISB '21 (WA) Kenan-Flagler '22 (WA) Yale '22 (D) Johnson '22 (WL)
GMAT 1: 720 Q47 V42
GPA: 3.4
Send PM
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   17 Aug 2018, 16:08
PKN wrote:
Bunuel wrote:
Chu-Li has $100 in her piggy bank. How much will she have in her bank 40 weeks from now if she puts $1 in the bank next week, $2 two weeks from now, $3 three weeks from now, and continues to increase the amount that she puts in by $1 each week?

A. $140
B. $800
C. $920
D. $1640
E. $1740


Cumulative amount of money in 40 weeks: 1+2+3+...............+40=\(\frac{40*41}{2}\)=820

Total savings=Base deposit+Additional deposit in 40 weeks=100+820=$920

Ans. (C)


Hi, what formula is this through which we get 40*41/2?

Posted from my mobile device
User avatar
D
PKN
Director
Director
Joined: 01 Oct 2017
Status:Learning stage
Posts: 827
Own Kudos [?]: 1298 [3]
Given Kudos: 41
WE:Supply Chain Management (Energy and Utilities)
Send PM
Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   17 Aug 2018, 21:08
2
Kudos
1
Bookmarks
vedanths wrote:
PKN wrote:
Bunuel wrote:
Chu-Li has $100 in her piggy bank. How much will she have in her bank 40 weeks from now if she puts $1 in the bank next week, $2 two weeks from now, $3 three weeks from now, and continues to increase the amount that she puts in by $1 each week?

A. $140
B. $800
C. $920
D. $1640
E. $1740


Cumulative amount of money in 40 weeks: 1+2+3+...............+40=\(\frac{40*41}{2}\)=820

Total savings=Base deposit+Additional deposit in 40 weeks=100+820=$920

Ans. (C)


Hi, what formula is this through which we get 40*41/2?

Posted from my mobile device


Hi vedanths,

The sum of first 'n' natural numbers:\(\frac{n(n+1)}{2}\)

Here we have to determine the sum of first 40 natural numbers,(1+2+...+40)
Now put n=40 in the above sum formula.We have ,sum=40*(40+1)/2.

Hope it helps.
avatar
B
vdsmba
Intern
Intern
Joined: 03 Sep 2017
Posts: 43
Own Kudos [?]: 8 [0]
Given Kudos: 57
Location: India
Schools: Anderson '22 (M) Darden '22 (D) Kellogg '22 (WL) Ross '22 (D) ISB '21 (WA) Kenan-Flagler '22 (WA) Yale '22 (D) Johnson '22 (WL)
GMAT 1: 720 Q47 V42
GPA: 3.4
Send PM
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   18 Aug 2018, 02:45
PKN wrote:
Hi vedanths,

The sum of first 'n' natural numbers:\(\frac{n(n+1)}{2}\)

Here we have to determine the sum of first 40 natural numbers,(1+2+...+40)
Now put n=40 in the above sum formula.We have ,sum=40*(40+1)/2.

Hope it helps.


Yes got it, thank you!
User avatar
L
CrackverbalGMAT
GMAT Club Legend
GMAT Club Legend
Joined: 03 Oct 2013
Affiliations: CrackVerbal
Posts: 4946
Own Kudos [?]: 7626 [0]
Given Kudos: 215
Location: India
Send PM
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   21 Nov 2020, 13:11
Top Contributor
Initial deposit = $100
Cumulative deposit over 40 weeks = (1+2+3+4+....40)$
= 40 * 41 /2 = 820
[ As we know,1+2+3+4+.....n =n(n+1) / 2 ]
Thus total deposits of Chu-Li = (100+820)$
=920$ (C)
Hope this helps :)
User avatar
G
CEdward
VP
VP
Joined: 11 Aug 2020
Posts: 1262
Own Kudos [?]: 201 [0]
Given Kudos: 332
Send PM
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   21 Nov 2020, 21:14
It took me longer than it should have to figure this out, but this was my approach.

Every number 1 through 9 appears 4 times so 4 x each digit 1 through 9 is:
4 + 8 + 12 + 16 + 20 + 24 + 28 + 32 + 36 = 180
10, 20, 30 each appear 10 times
(10 x 10) + (10 x 20) + (10 x 30) = 600
40 appears once:
40

600 + 180 + 40 + 100 (original amount) = 920.
User avatar
G
karnavora1
Manager
Manager
Joined: 29 Feb 2020
Posts: 80
Own Kudos [?]: 91 [0]
Given Kudos: 13
Location: India
Concentration: Marketing, International Business
Schools: Rotman '22 ISB'22 Goizueta "23
GMAT 1: 600 Q42 V31
Send PM
Reviews Badge
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   21 Nov 2020, 22:13
Answer: C

There are 2 ways this can be solved

With the formula Sum=\(\frac{n(n+1)}{2}\)

Sum=\(\frac{40(40+1)}{2}\)=820

The other way is slightly longer but involves identifying a pattern
Let's take the first 5 weeks
1+2+3+4+5=15
The next 5 weeks
6+7+8+9+10=40
The next 5 weeks
11+12+13+14+15=65
The next 5 weeks
16+17+18+19+20=90

If you notice the increments are of 25, we can just add up the numbers now and come to the answer.
This method is best used when then numbers are small, otherwise it might take a very long time to reach the answer.
avatar
S
sm1510
Manager
Manager
Joined: 22 Aug 2010
Posts: 53
Own Kudos [?]: 117 [1]
Given Kudos: 332
Send PM
GMAT ToolKit User
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   01 Dec 2021, 02:54
1
Kudos
seen in gmat prep - exam 6
User avatar
L
Bunuel
Math Expert
Joined: 02 Sep 2009
Posts: 92900
Own Kudos [?]: 618840 [0]
Given Kudos: 81588
Send PM
CAT Tests Forum Quiz Mode
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   01 Dec 2021, 03:01
Expert Reply
sm1510 wrote:
seen in gmat prep - exam 6


_______________________
Added the tag. Thank you!
avatar
B
Dhwanii
Manager
Manager
Joined: 16 Mar 2021
Posts: 79
Own Kudos [?]: 10 [0]
Given Kudos: 96
Send PM
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   04 Jan 2022, 00:56
What we have done is (1+2+3+4...+40)+ 100 as it is 40 weeks but qs stem says person will deposit $1, 1 week from so this very week there's no deposit leaves us w only 39 weeks to deposit money so it should be (1+2+3...39) isn't it ? Any experts,kindly help

Posted from my mobile device
User avatar
bumpbot
Non-Human User
Joined: 09 Sep 2013
Posts: 32658
Own Kudos [?]: 821 [0]
Given Kudos: 0
Send PM
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] New post   22 Apr 2023, 03:35
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
GMAT Club Bot
gmatclubot
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink]
22 Apr 2023, 03:35
Moderators:
Bunuel
Math Expert
92900 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