So represent number as xy remember that since x is in the tens place, the value of the number is 10x+y x+y=7 if 9 is subtracted from (10x+y), then the answer will be the number with the digits reversed (10y+x) find the number
x+y=7 (10x+y)-9=(10y+x) 10x+y-9=10y+x subtract x from both sides 9x+y-9=10y subtract y from both sides 9x-9=9y add 9 to both sides 9x=9y+9 9(x)=9(y+1) divide both sides by 9 x=y+1 we also have x+y=7 isolate x by subtracting y from both sides x=7-y subsitute (7-y) for x in othe requation 7-y=y+1 add y to both sides 7=2y+1 subtract 1 from both sides 6=2y divide both sides by 2 3=y
subsitute x+y=7 x+3=7 subtract 3 from both sides x=4 number=10x+y 10(4)+3 40+3 43 the number is 43
