1.

The sum of the digit of a 2- digit number is 6 times the unit digit. Find the number.

Answer»

Set t = the tens digit
U = the unitis digit
t + u = 9
Solve for t by adding -u to each SIDE.
t = 9 - u
The value of the number is 10T + u.
(10t + u) = 6u
Substitute (9 - u) for t in the above
10(9 - u) + u = 6u
90 - 10u + u = 6u
90 - 9u = 6u
add 9u to each side
90 = 15u
divide each side by 15
6 = u
since t+u = 9
t + 6 = 9
add -6 to each side
t = 3
Since t+u = 9, 3+u = 9 and u = 6
So our number is 36


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