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unique odd digits

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unique odd digits

by umaa » Mon Jul 21, 2008 6:22 am
Say A, B and C represent unique odd digits. Then take a look at the following multiplication problem: ABA * B = CBB. Which of these can represent the number ABA?

A. 171
B. 353
C. 313
D. 151
E. 121

Please let me know the answer
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by reachac » Mon Jul 21, 2008 6:31 am
IMO D

Just plugged in the options.
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by VP_Tatiana » Mon Jul 21, 2008 6:35 am
We want to figure out which number, when multiplied by the single digit in its tens position, will result in:

1) A 3 digit number
2) A number with the same units and tens digit

I notice that B and D have tens digit 5. I think they are good possibilities to fit the bill, since 5*odd number always ends in 5 (and we know all of the digits are odd.) This makes it highly likely that the last two digits will be the same.

First I try B, 353. I want to work out 353*5. I remember that 333.333*3 = 1000. Since both parts of the product 353*5 are bigger than that, we know this results in something over 1000. This does not fit the bill since it is not a 3 digit number.

Now I try D, 151. I line up the multiplication problem:

151
X 5

I see I get a 5 in the units digit, then a 5 in the tens digit... I don't need to worry about carrying the 2 or going any further because I know this is a 3 digit number whose last two digits are the same.

So, the answer is D.
Tatiana Becker | GMAT Instructor | Veritas Prep
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by umaa » Mon Jul 21, 2008 6:35 am
can you please explain me. I'm getting 171.

19*3*3
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Re: unique odd digits

by parallel_chase » Mon Jul 21, 2008 6:37 am
umaa wrote:Say A, B and C represent unique odd digits. Then take a look at the following multiplication problem: ABA * B = CBB. Which of these can represent the number ABA?

A. 171
B. 353
C. 313
D. 151
E. 121

Please let me know the answer
The answer is 151, you simply have to look at the answer options.

Lets start with 171*7=something 9 7

353*5 = something 6 5

151 * 5 = 755
ABA * B = CBB

The long way is ABA*B= CBB

A*B = B has to be in the units place, therefore A has to be 1

1B1 * B = CBB

B*B = B is in the units place, therefore only integer possible is 5

151*5 = C55

I hope this clears everything.
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by umaa » Mon Jul 21, 2008 6:39 am
got it. thx.
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