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17 Aug 2018, 12:26
00:00

Difficulty:

15% (low)

Question Stats:

78% (01:17) correct 22% (01:19) wrong based on 65 sessions

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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

_________________
Director
Joined: 20 Feb 2015
Posts: 733
Concentration: Strategy, General Management
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] ### Show Tags 17 Aug 2018, 12:41 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 Director Status: Learning stage Joined: 01 Oct 2017 Posts: 857 WE: Supply Chain Management (Energy and Utilities) Re: Chu-Li has$100 in her piggy bank. How much will she have in her bank  [#permalink]

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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) _________________ Regards, PKN Rise above the storm, you will find the sunshine Intern Joined: 03 Sep 2017 Posts: 10 Location: India GMAT 1: 700 Q44 V42 GPA: 3.4 Re: Chu-Li has$100 in her piggy bank. How much will she have in her bank  [#permalink]

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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 Director Status: Learning stage Joined: 01 Oct 2017 Posts: 857 WE: Supply Chain Management (Energy and Utilities) Chu-Li has$100 in her piggy bank. How much will she have in her bank  [#permalink]

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17 Aug 2018, 21:08
1
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. _________________ Regards, PKN Rise above the storm, you will find the sunshine Intern Joined: 03 Sep 2017 Posts: 10 Location: India GMAT 1: 700 Q44 V42 GPA: 3.4 Re: Chu-Li has$100 in her piggy bank. How much will she have in her bank  [#permalink]

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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!
Target Test Prep Representative
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2835
Re: Chu-Li has $100 in her piggy bank. How much will she have in her bank [#permalink] ### Show Tags 20 Aug 2018, 11:05 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 _________________ Jeffery Miller Head of GMAT Instruction GMAT Quant Self-Study Course 500+ lessons 3000+ practice problems 800+ HD solutions Re: Chu-Li has$100 in her piggy bank. How much will she have in her bank &nbs [#permalink] 20 Aug 2018, 11:05
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