TITLE: What inequality does the units digit of a two digit number less than $40$ satisfy if the sum of the units digit and tens digit equals $8$?
QUESTION [2 upvotes]: For a two digit number , the sum of the "units digit" and "tens digit" is $8$ and the two-digit number is less than $40$.
Denoting that the "units digit" of the two-digit number to be $x$, form an inequality and solve for $x$.
I'm not sure how to find the "tens digit" as I have problems understanding the question .
Thanks for helping ..

REPLY [0 votes]: Let $t$ denote the tens digit; let $x$ denote the units digit.  Since the sum of the tens digit and the units digit is $8$, 
$$t + x = 8$$
Since the two-digit number is less than $40$, $1 \leq t \leq 3$.  Since 
$$x = 8 - t$$
you can determine the possible values of $x$.
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