I think Julia has given a great answer.
I would add that when doing calculations (whether by hand or with a calculator), if you have time, it is often a good idea to do a quick mental check whether your answer seems reasonable by comparing it to what you would expect if you just guessed using rough calculation.
For example, this question could be read like this : "What is the product of some number a little less than five and another number almost as big as one quarter?" When viewed this way, the question is almost the same thing as "What is five divided by four?" ... because multiplying by one over a value is equivalent to dividing by that value.
Keeping in mind that because both of the actual factors were smaller than this rough equivalent we'd expect our answer to be a little smaller than 1.25. If you had put the decimal point in the wrong spot, you won't be close to that (you'll typically be off by at least a factor of roughly ten) and at least with this type of common mistake, you'd be alerted that something was wrong.
The best thing is to avoid mistakes in the first place, but training your ability to detect mistakes intuitively can also pay off.