Some ways of simplifying calculations :

This is a very simple method. You may feel that adopting this method will only save 5 seconds and wonder how you will benefit by it. If you adopt such methods at a number of places in the full paper and you can save even 5 or 6 minutes it will help you attempt at least 6 to 8 more questions. This itself may make all the different to your chances of selection in any competitive exam.

For multiplication by 5, you should multiply the figure given by 10 and then divide it by 2.

e.g. 12986 × 5 = 129860/2 = 64930.

For multiplication by 25, you should multiply the figure given by 100 and then divide it by 4.

e.g. 12986 × 25 = 1298600/4 = 324650.

For multiplication by 125, you should multiply the figure given by 1000 and then divide it by 8.

e.g. 12986 × 125 = 12986000/8 = 1623250.

For multiplication by 625, you should multiply the figure given by 10000 and then divide it by 16.

e.g. 12986 × 625 = 129860000/16 = 8116250.

Alternatively, you can treat 125 as 100 + 25. So, multiplication by 125 can be treated as multiplication by 100 and to this figure ¼ of itself (25 is ¼ of 100).