Renu L.

asked • 05/15/17

Maths linear equation in one variable

solve - a two digit number is such that one digit is twice the other. on interchanging the digit the new number so obtained is less  than 9 and twice the orginal number. Find the original number.

Ravi V.

I think you meant to say "so obtained is 9 less than twice the original number"
 
If so, the answer would be 36. as 63 is 9 less than 36*2 = 72
 
If you want to solve this mathematically, there are two cases. I will do one.
Let's say the number is formed by two digits X and 2X. In our answer for example X is 3 and 2X is 6.
 
So in general representation, the original number is 10*X+1*2X assuming X is in the 10th place and 2X is in the units place.
 
So original number is 12X
New number formed by interchanging the digits will have a value of 10*2X + X = 21X
We are given that the new number is 9 less than twice the original number.
So, 12X*2 -9 = 21X
Or 24X -9 = 21X
i.e. 3X -9 = 0
X = 3 
So, your original number X,2X = 36
 
You can try the case where original number is 2X,X, i.e. the bigger number is in 10th place if you want and see what happens using similar logic.
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05/15/17

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Ravi V. answered • 05/15/17

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There are too many valid answers. For example
12
 
Twice 12 is 24 and it is greater than the number formed by interchanging digits is 21 and is less than 24
Ofcourse 21 also has the same property.
 
So does 24 (note 42 < 48) and 42 is also a valid answer as 24 < 84
 
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Renu L.

sorry I forget to write 9 inthe question but now i have edit my question
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05/15/17

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