Question

The sum of the digits in a two digit number is 9. If the digits are reversed, the new number will be 9 less than the original number. What is the original number?

Answer 1

let the digits be x and y
x+y= 9
x=9-y
hence the number would be
10(9-y)+y is the number
now if the digits are reversed we got
10y+ (9-y)
since y would be tens digit hence we would multiply it with 10
now see it is given that
10(9-y) + y - (10y + 9-y)
90-10y + y - 9y - 9
81 -18y = 9
-18y = 9 -81
-18y = -72
y = -72/-18
y=4
so the digits are 9-y and y
one is 4 and the other one is (9-4) = 5
the original number was 45 understood if any other problem tell me

Answer 2

also, 12 and 21 work

Answer 3

yes alex

Answer 4

i find the easiest method for these is to brute logic them. but it is important to learn the equations and understand the principles behind them

Answer 5

yes u r right alex

Answer 6

alex how does 12 and 21 work?? sum of digits must be 9...

Answer 7

yes KBOY is also right alex 12 and 21 is not the posssible answer