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Question 1110865: For every positive 2-digit number, x, with tens digit t and unit digit u, let y be the 2-digit number formed by reversing the digits of x. Which of the expressions is equivalent to x-y? And explain why otherwise no points.
A. 9 (t - u)
B. 9 (u - t)
C. 9t - u
D. 9u - t
E. 0
Answer by jim_thompson5910(35256)   (Show Source):
You can put this solution on YOUR website! x is some two digit number with t as the tens digit and u as the units digit
So this means,
x = 10t+u
Example: t = 5 and u = 3, so x = 10t+u = 10*5+3 = 53
In contrast,
y = 10u+t
because the tens and units digits have been swapped
Subtract x and y
x-y = (10t + u) - (10u + t)
x-y = 10t + u - 10u - t
x-y = (10t - t) + (u - 10u)
x-y = 9t - 9u
x-y = 9(t-u)
Which is why the answer is choice A
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