Is 11/20 and 17/40 and 1/12 either a repeating decimal or a terminating?

Every decimal is either repeating or terminating.  
It has to be one or the other.

1/12 is repeating.
The others terminate.

A fraction is a short way to write a division problem.

Whenever you see a fraction, it means

     (the top number)  divided by  (the bottom number).

When you pick up your pencil or your calculator and actually do
the division, the answer to the division is the decimal form of the
fraction.   There you can see whether it’s terminating or repeating.

To find the decimal form of  11/20, divide  11  by  20.  It’s  0.55.

To find the decimal form of  17/40, divide  17  by  40.  It’s  0.425.

To find the decimal form of  1/12, divide  1  by  12.  It’s 0.08333. repeating.