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Eight light bulbs numbered 1 through 8 are arranged in a circle as sho

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Eight light bulbs numbered 1 through 8 are arranged in a circle as sho  [#permalink]

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New post 26 Apr 2019, 07:10
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Question Stats:

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Eight light bulbs numbered 1 through 8 are arranged in a circle as shown above. The bulbs are wired so that every third bulb, counting in a clockwise direction, flashes until all bulbs have flashed once. If the bulb numbered 1 flashes first, which numbered bulb will flash last?

A. 2
B. 3
C. 4
D. 6
E. 7


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Quantitative Review 2020 NEW QUESTION

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2019-04-26_1808.png
2019-04-26_1808.png [ 12.37 KiB | Viewed 1252 times ]

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Re: Eight light bulbs numbered 1 through 8 are arranged in a circle as sho  [#permalink]

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New post 26 Apr 2019, 07:37
1
The sequence of flashing would be:
1 -> 4 -> 7 -> 2 -> 5 -> 8 -> 3 -> 6

so D
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Re: Eight light bulbs numbered 1 through 8 are arranged in a circle as sho  [#permalink]

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New post 28 Apr 2019, 04:40
logical question
draw fig and solve
we see bulb 6 flashes last
IMO D

Bunuel wrote:
Image
Eight light bulbs numbered 1 through 8 are arranged in a circle as shown above. The bulbs are wired so that every third bulb, counting in a clockwise direction, flashes until all bulbs have flashed once. If the bulb numbered 1 flashes first, which numbered bulb will flash last?

A. 2
B. 3
C. 4
D. 6
E. 7


PS56602.01
Quantitative Review 2020 NEW QUESTION

Attachment:
2019-04-26_1808.png

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Re: Eight light bulbs numbered 1 through 8 are arranged in a circle as sho  [#permalink]

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New post 01 May 2019, 05:56
How can all bulbs flash
The question says that every third bulb will flash. So If it starts from bulb no 1 then the third bulb will be bulb no 3
How can the third bulb be no 4
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Re: Eight light bulbs numbered 1 through 8 are arranged in a circle as sho  [#permalink]

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New post 01 May 2019, 06:11
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devavrat wrote:
How can all bulbs flash
The question says that every third bulb will flash. So If it starts from bulb no 1 then the third bulb will be bulb no 3
How can the third bulb be no 4

I hope to help you with this.
In general, every third means that the difference is 3

on a number line, every third number is 3,6,9,..... --> if the initial integer is 0
but if the initial integer is 1, then the sequence is 4,7,10,...

if you assume a sequence of 1,3,6,9,.. ---> it will be an incorrect sequence as the difference between the second and the first is not equal the difference between the third and the second.
if you assume a sequence of 1,3,5,... ---> it will be a sequence of every second number (as the difference is 2)

in other words: if the bulb no. 1 is not the first to flash, then the first one to flash will be bulb no. 3 followed by 6.
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Re: Eight light bulbs numbered 1 through 8 are arranged in a circle as sho  [#permalink]

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New post 07 May 2019, 02:48
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Ans: just deduct 3 places from First bulb, because flashing will stop before it reaches the first bulb.
( save time if lot of numbers are present)
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Re: Eight light bulbs numbered 1 through 8 are arranged in a circle as sho  [#permalink]

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New post 07 May 2019, 02:52
Bunuel wrote:
Image
Eight light bulbs numbered 1 through 8 are arranged in a circle as shown above. The bulbs are wired so that every third bulb, counting in a clockwise direction, flashes until all bulbs have flashed once. If the bulb numbered 1 flashes first, which numbered bulb will flash last?

A. 2
B. 3
C. 4
D. 6
E. 7


PS56602.01
Quantitative Review 2020 NEW QUESTION

Attachment:
2019-04-26_1808.png


I would like to do it in manual way

Lighting happens like this

1, 4, 7, 2, 5, 8, 3, 6

i.e. Bulb 6 flashes last

Answer: Option D
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Re: Eight light bulbs numbered 1 through 8 are arranged in a circle as sho  [#permalink]

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New post 22 May 2019, 17:51
"The bulbs are wired so that every third bulb, counting in a clockwise direction, flashes until all bulbs have flashed once. If the bulb numbered 1 flashes first, which numbered bulb will flash last?"

Every third bulb means that the number 1 bulb would be counted as 0... and we would move 3 spaces to number 4 and repeat until none are left. In other words, Last-First + 1 ... would be 4th bulb - 1st bulb + 1 = 3 spaces moved. Repeat until finished.
I drew a diagram and just crossed out the successive bulbs.
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Re: Eight light bulbs numbered 1 through 8 are arranged in a circle as sho  [#permalink]

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New post 23 May 2019, 06:51

Solution


Given
In this question, we are given
    • Eight light bulbs numbered 1 through 8 are arranged in a circle, as shown in the diagram.
    • The bulbs are wired so that every third bulb, counting in a clockwise direction, flashes until all bulbs have flashed once.
    • The bulb numbered 1 flashes first.

To Find
We need to determine
    • The number of the bulb that will flash last.

Approach & Working
As every third bulb is flashing, starting from bulb 1, we can determine the next bulbs as follows
    • First: Bulb 1
    • Second: Bulb 4
    • Third: Bulb 7
    • Fourth: Bulb 2
    • Fifth: Bulb 5
    • Sixth: Bulb 8
    • Seventh: Bulb 3
    • Eighth: Bulb 6

As we can see, all the eight bulbs are flashing at least once, and the last one to flash is bulb 6.

Hence, the correct answer is option D.

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Re: Eight light bulbs numbered 1 through 8 are arranged in a circle as sho  [#permalink]

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New post 23 May 2019, 17:13
Bunuel wrote:
Image
Eight light bulbs numbered 1 through 8 are arranged in a circle as shown above. The bulbs are wired so that every third bulb, counting in a clockwise direction, flashes until all bulbs have flashed once. If the bulb numbered 1 flashes first, which numbered bulb will flash last?

A. 2
B. 3
C. 4
D. 6
E. 7


PS56602.01
Quantitative Review 2020 NEW QUESTION

Attachment:
2019-04-26_1808.png


So the bulbs will flash in the following order:

1, 4, 7, 2, 5, 8, 3 ,6

Answer: D
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Re: Eight light bulbs numbered 1 through 8 are arranged in a circle as sho   [#permalink] 23 May 2019, 17:13
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