FDP Chapter 1, Question 11

[francesca.lanata]

It may be a silly question, but I am a bit confused about Chapter 1 question 11 on the GMAT Strategy Guide. I understand that you are to re-write A and B using x and y digits, but why is A=10X+Y and B=10Y+X? Where does this formula come from?

Thanks!

[karan13]

consider any 2 digit no..... say 23 .... how will you get this value... go back to basic maths.. the tens digit is 2 and one digit is 3 that technically means that 2X10+3X1=20+3=23 .. is you consider tens place digit as x and ones place digit as y you can make a general formula 10x+y.Also note when you reverse the digits you will get 10y+x.... hope this helps.. take a few examples like 23 to figure it out ..

[francesca.lanata]

Ah, ok, I see. I thought it was a matter of plugging those values into the Q=10B-A, which now I see isn't right. Thanks!!

[jnelson0612]

Thanks karan!