Question

the sum of the digits of a 2-digit number is 7.If the digits are reversed, the number formed is 9 less than the original number. what is the original number

Answer 1

let x be in tenths place and y be in units place

given sumof the digits is 7 so,x+y=7......

The desired no. is 10x+y(original no.),if we reverse them we get 10y+x(new no.)

Acc.to question,

x+y=7.....

10y+x=10x+y-9

9y-9x=-9

y-x=-1

or,y=x-1

putting the value of y in eqn x+y=7, we get

x+x-1=7

2x=8

x=4

y=4-1=3

the no 10x+y=10×4+3=43 is the no.