Question 371177
This question is a tricky one =] It almost stumped me. You can let the two digit number be xy, with x=the number in the tens digit and y= the number in the ones digit. Now we can write equations using the information from the problem. The sum of the digits is 7: {{{x+y = 7}}}. If 9 is subtracted from the number, the answer will be a number with the digits reversed: {{{xy-9=yx}}}. We have found our equations. We move onto the solving part. Now the trick is to add yx to both side of this equation, so {{{xy-9=yx}}} becomes {{{xy+yx-9=yx+yx}}}. Adding together xy+yx is like adding the x+y (tens digit) and the y+x (ones digit) together. We know from the first equation that x+y=7, so xy+yx=77! So, {{{xy+yx-9=yx+yx}}} becomes {{{77-9=yx+yx}}}. yx+yx=2yx (because you have two of one thing. The equation then becomes {{{77-9=2yx}}}, then you get {{{68=2yx}}}. Divide both sides by 2 to get {{{34=yx}}}. So, y=3 and x =4. So, the number is 43 (because our number is xy). I hope this helps! Please visit my website at www.myonlinetutor.webs.com to get help with homework problems! =] Thanks!