Question

a number consists of two digits whose sum is 7.If 45 is added to the number ,the digits are reversed.Find the number

Answer 1

let the number be xy

x + y = 7 ---------(1)

10x + y + 45 = 10y + x

9y - 9x = 45

y - x = 5

y = 5 + x ---------(2)

solving equation 1 and 2

x + 5 + x = 7

2x = 2

x = 1

putting value of x in (1)

x + y = 7

1 + y = 7

y = 6

the number is 16

Answer 2

Answer:

let \: the \: ones \: digit \:  = x \\ and \: tens \: digit \:  = y \\ so \: the \: number \:  = 10y + x \\ according \: to \: question \: x + y = 8..........(1) \\ and \: if \: added \: 18 \: the \: number \:  =>  10y + x  + 18 = 10x + y \\  = > 9y - 9x =  - 18 \\  => 9x - 9y = 18..........(2) \\ (1) \times 9 => 9x + 9y = 72........(3) \\ (3) - (2) => 18y = 54 \\ so \: y = 3 \\ and \: from \: (1) \: x = 5 \\ hence \: the \: number \: is \:  = 10y + x = 10 \times 3 + 5 = 35

Step-by-step explanation: