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# A certain drive-in movie theater has total of 17 rows of parking space

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Math Expert
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A certain drive-in movie theater has total of 17 rows of parking space [#permalink]

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03 Jul 2016, 10:26
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A certain drive-in movie theater has total of 17 rows of parking spaces. There are 20 parking spaces in the first row and 21 parking spaces in the second row. In each subsequent row there are 2 more parking spaces than in the previous row. What is the total number of parking spaces in the movie theater?

A) 412
B) 544
C) 596
D) 632
E) 692
[Reveal] Spoiler: OA

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Re: A certain drive-in movie theater has total of 17 rows of parking space [#permalink]

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03 Jul 2016, 10:37
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Bunuel wrote:
A certain drive-in movie theater has total of 17 rows of parking spaces. There are 20 parking spaces in the first row and 21 parking spaces in the second row. In each subsequent row there are 2 more parking spaces than in the previous row. What is the total number of parking spaces in the movie theater?

A) 412
B) 544
C) 596
D) 632
E) 692

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Re: A certain drive-in movie theater has total of 17 rows of parking space [#permalink]

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03 Jul 2016, 23:03
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596

first row 20 then other 16 rows form an Ap with first term 21 and last 51.Avg is 36
so 36*16+20=596
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Re: A certain drive-in movie theater has total of 17 rows of parking space [#permalink]

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10 Jul 2016, 16:19
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A certain movie theater has a total of 17 rows of parking space

Number of parking Spaces in first row 20
Number of parking Spaces in first row 21
Number of parking Spaces in first row 23

It is evident that from Second row the other 16 rows form an Airthematic Progression with first term 21
The last term of AP i.e $$T16$$ = 21+(16-1)*2 = 51.
Sum of Arithmetic series =16*(51+21)/2 = 576

The sum of the series = 576+20

so 36*16+20=596

Hence Option C
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Re: A certain drive-in movie theater has total of 17 rows of parking space [#permalink]

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10 Aug 2016, 18:47
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Attached is a visual that should help.
Attachments

Screen Shot 2016-08-10 at 7.45.53 PM.png [ 155.8 KiB | Viewed 5220 times ]

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A certain drive-in movie theater has total of 17 rows of parking space [#permalink]

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16 Oct 2016, 03:56
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First Row = 20

Second Row =21

Third Row = 21 + 2

Fourth Row = 21 + 4

Third till Last Row are in a sequence with difference of 2 between each terms. Hence, Sum of all terms in this sequence of 15 terms = N/2 * (2* First Term + {n-1} * Difference) = 15/2 * (2*23 + 14*2) = 555

Sum of all terms = 20 + 21 + 555 = 596
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A certain drive-in movie theater has total of 17 rows of parking space [#permalink]

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07 May 2017, 05:43
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Bunuel wrote:
A certain drive-in movie theater has total of 17 rows of parking spaces. There are 20 parking spaces in the first row and 21 parking spaces in the second row. In each subsequent row there are 2 more parking spaces than in the previous row. What is the total number of parking spaces in the movie theater?

A) 412
B) 544
C) 596
D) 632
E) 692

we are dealing with consecutive integers!

therefore average=median

first two rows = 20+21 = 41

next 15 rows --> Median = (23,25,27,29,31,33,35,37,39,41,43,45,47,49,51) we can stop listing them down at 37, since median = 8th term

Hence, 41 + 37*15 = 596
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A certain drive-in movie theater has total of 17 rows of parking space [#permalink]

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07 May 2017, 06:13
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First row will have 20 parking spaces.
Second column onwards is an AP with
Starting term(a) = 21
Common difference(d) = 2
Number of terms(n) = 16

Sum of n terms(Sn) = $$\frac{n}{2}*(2a + (n-1)d)$$

Substituting the values,
Sn = $$\frac{16}{2}*(2*21 + (16-1)2)$$
= 8 * (42+30)
= 8 * 72
= 576

Total number of parking spaces are 20+576 = 596(Option C)
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A certain drive-in movie theater has total of 17 rows of parking space [#permalink]

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09 Jun 2017, 14:36
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Bunuel wrote:
A certain drive-in movie theater has total of 17 rows of parking spaces. There are 20 parking spaces in the first row and 21 parking spaces in the second row. In each subsequent row there are 2 more parking spaces than in the previous row. What is the total number of parking spaces in the movie theater?

A) 412
B) 544
C) 596
D) 632
E) 692

20+16*[21+(21+15*2)]/2=596 total spaces
C
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Joined: 23 Nov 2016
Posts: 5
Re: A certain drive-in movie theater has total of 17 rows of parking space [#permalink]

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07 Jul 2017, 11:31
MENNAWALID wrote:

Posted from my mobile device

I believe you are searching for a formula.
This one is a simple AP formula.

Sum= n/2{2a+(n-1)d}
here a=21
n=16
d=2

So now we get = 16/2{2*21+(16-1)*2}
=> 16(21+15)
=> 16*36
=> 576
Add the 20 from the first row to get 596 as your total.
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Re: A certain drive-in movie theater has total of 17 rows of parking space [#permalink]

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16 Dec 2017, 02:25
Bunuel wrote:
A certain drive-in movie theater has total of 17 rows of parking spaces. There are 20 parking spaces in the first row and 21 parking spaces in the second row. In each subsequent row there are 2 more parking spaces than in the previous row. What is the total number of parking spaces in the movie theater?

A) 412
B) 544
C) 596
D) 632
E) 692

Total Rows : 17
Info given on 1st two Rows : 20, 21 Spaces .

Rest of the spaces will increase per row by 2 spaces. Hence this becomes an AP question.

17-2= 15 Rows
First term= 21
]Last term = (No of Rows * Difference) + First Term= 15*2=30

Therefore AP is 21.....51
No of rows for AP = [51-21]/2 +1=16

Sum of AP= Mean * No of terms involved in AP
= [51+21]/2 * 16= 576

Now we have 20 Spaces from firt Row therefore total spaces = 576 +20=596

The only difficulty you might face is figuring out why first 15 rows were used and then 16.
15 were used from 3rd to 17th row. Because we had info of 2nd row. (i.e. 21 spaces)

While in AP, we used info from 2nd row to 17th, hence 16 rows.

Easier of way finding a mean for AP is via Median
,23,25.....51. Middle term is 37
Sum of AP becomes : 37 * 15 = 555
Now add first 2 row spaces = 555 + 20+21= 596.
Re: A certain drive-in movie theater has total of 17 rows of parking space   [#permalink] 16 Dec 2017, 02:25
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