Trick for number 5

Multiples of 5 include: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, ...

Common method of multiplying numbers by 5:

 Another technique in dealing with multiplication by 5 (which I often use to make it easier for me to solve this mentally) is:

Choose for yourself which is easier then try doing it mentally.

In dealing with odd numbers, I usually convert it to an even number first by multiplying it with 10 before dividing it by 2.