In the multiplication above, $\#$ represents a single digit. What digit does $\#$ represent?

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Gmat_mission: Legendary Member; Posts: 1622; Joined: Thu Mar 01, 2018 7:22 amFollowed by: 2 members

by Gmat_mission » Thu Sep 10, 2020 12:58 am

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2018-11-13_1250.png

In the multiplication above, $\#$ represents a single digit. What digit does $\#$ represent?

A. 2
B. 3
C. 4
D. 5
E. 6

Answer: D

Source: Princeton Review

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Source: Beat The GMAT — Problem Solving | Thu Sep 10, 2020 12:58 am

ravinikhil: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Thu Sep 10, 2020 6:03 am

Re: In the multiplication above, $\#$ represents a single digit. What digit does $\#$ represent?

by ravinikhil » Thu Sep 10, 2020 6:22 am

The final number must be of the form 2 XX0 and must be a divisible by 510.
since both the nos involved have 0 at the end , lets divide both by 10 and get rid of the extra 0's.
thus the no now is 2XX and 51.
now lets just add 51,
51,102,153,204,255.
bingo !
we get 255 which is of the form 2XX.
Hence X is 5.
to verify just put in the pic given, 510 * 5 = 2550 .
should not take more than 30 seconds

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Re: In the multiplication above, $\#$ represents a single digit. What digit does $\#$ represent?

by Scott@TargetTestPrep » Mon Sep 14, 2020 3:50 am

Gmat_mission wrote: ↑
Thu Sep 10, 2020 12:58 am
2018-11-13_1250.png

In the multiplication above, $\#$ represents a single digit. What digit does $\#$ represent?

A. 2
B. 3
C. 4
D. 5
E. 6

Answer: D

Solution:

We see that when a number in the low 500s is multiplied by a single digit number, the product is in the 2000s. Therefore, that single digit number must be either 4 or 5.

If it’s 4, then we have 510 x 4 = 2040. However, this is not correct, given that the pound sign (#) can only represent one unique digit.

If it’s 5, then we have 510 x 5 = 2550. We see that # must be 5.

Answer: D

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