Question

the sum of the digits of two digit number is 9. the number is 6 times the unit digit. find the number

Answer 1

According to me the number is 36.
set t=the tens digit
u=the units digit
t+u=9
the value of number is 10t+u
(10t+u)=6u
substitute(9-u)from t in the above
10(9-u)+u=6u
90-10u+u=6u
90-9u=6u
add 9u to both sides
90=15u
divide each side by 15
6=u
since t+u=9
t+6=9
add -6to each side
t=3
since t+u=9,3+u=9,and u=6
So our number is 36.

Answer 2

The sum of two digit number is 9.
t + u = 9
u = (9-t)
The number is 6 times the unit digit.
10t + u = 6u
10t + u - 6u = 0
10t - 5u = 0
10t - 5(9-t) = 0
10t - 45 + 5t = 0
10t + 5t = 45
15t = 45
t = 45/15
t = 3 is the tens digit
then
9-3 = 6 is units digit
the number is 36

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