the sum of the digits of a certain two-digits number is 7.Reversing its digits increases the number by 9.What is the number
The answer is 34. 3+4=7. 43-34=9. I hope this helps.
unit digit=y tens digit=x the number: 10x+y We suggest this system of equations: x+y=7 (10y+x)=(10x+y)+9 we solve it by substitution method. x=7-y 10y+(7-y)=(10(7-y)+y)+9 9y+7=70-10y+y+9 9y+10y-y=70+9-7 18y=72 y=72/18=4 x=7-y x=7-4=3 number=10x+y=10*3+4=30+4=34 solution: the number: 34 To check: 3+4=7 43=34+9