You'll like this -- it's really easy!

Take this decimal...

.7

What spot is that 7 in?

.7

So, put the 7 over 10:

.7 = 7/10

Done!

Here's another one:

                   .5 = 5/10  <-- Hey, this guy reduces!

.5 = 5/10 = (5/10) / (5/5) = 1/2

So,   .5 = 1/2