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# How many reversed two digit pairs are there such that three xy is x+y

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VP
Joined: 07 Dec 2014
Posts: 1224
How many reversed two digit pairs are there such that three xy is x+y  [#permalink]

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16 Jan 2019, 21:49
4
00:00

Difficulty:

55% (hard)

Question Stats:

53% (02:00) correct 47% (01:55) wrong based on 20 sessions

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How many reversed two digit pairs are there such that three xy is x+y less than yx?

A. 1
B. 2
C. 3
D. 4
E. 5
Director
Joined: 09 Mar 2018
Posts: 994
Location: India
Re: How many reversed two digit pairs are there such that three xy is x+y  [#permalink]

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16 Jan 2019, 22:22
gracie wrote:
How many reversed two digit pairs are there such that three xy is x+y less than yx?

A. 1
B. 2
C. 3
D. 4
E. 5

As per my understanding the question is
is 3 xy = yx - (x+y)

I tried using this approach in which i assumed a 2 digit number to be 10 y + x
3 (10 x + y) = 10y + x - x - y
10 x + y =3y
10 x = 2y
x = y/5

This means 10 y + y/5 is a 2 digit number
=> 51y/ 5 = 51 will be the only pair, for y = 5

Let me know if this approach is correct.

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Re: How many reversed two digit pairs are there such that three xy is x+y   [#permalink] 16 Jan 2019, 22:22
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