Question

a number consists of two digits whose sum is 9 if the digits are reversed the new number 3/8 of the first number find the number
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Answer 1

let the no. is 10x + y

x + y = 9 eq1

10y +x = 3/8 (10x +y)

80y + 8x = 30x + 3y

80y -3y = 30x - 8x

77y = 22x

Now from eq1 put x = 9 - y

77y = 22(9 - y)

77y = 198 - 22y

99y = 198

y = 2

put y in eq1

x + y = 9

x + 2 = 9

x = 7

Number is 10x + y

10×7+2= 70 + 2

number = 72