Eighty-one less than 8 times a number is 31. What is the number?

Let the number you need to determine be
X.

Now as eighty one less than 8 times the number is 31, we
can create an equation as follows:

eight times the number
is 8X

eighty one less than eight times the number is
8X-81

as this is equal to 31, we have
8X-81=31

=>8X = 81+31 =
112

=>X= 112/8 = 14

The
required number is 14.