Posted by Anonymous on .
The sum of the digits of a certain twodigit number is 7. Reversing its digits increase the number by 9. What is the number. Use x and y. Please help me!!!!

algebra 
Reiny,
in the original number, let the unit digit be x, then tens digiti be y
so the original number is 10y + x
where x+y = 7
the number reversed will be 10x + y
new number  old number = 9
10x + y  (10y + x) = 9
9x  9y = 9
or xy = 1
x+y=7
xy=1
add them
2x = 8
x = 4, then y = 3
the number is 10y+x = 34
check:
original number is 34
reversed number is 43
is the number increased by 9 ??? YES
is the sum of the digits 7 ??? YES
YEAHHH