In this post, we will show you how to do Subtractions Mentally. Have a look at the following examples....
- Instead of taking a single digit at a time, subtractions would be faster by taking two digits.... See here
- 87 - 56 = 31
- 900 - 200 = 700
- So, the result of 987 - 256 = 731
- Take
100s Complement of 87 (i.e. 100 - 87) which is 13 and add it to 24. The
result is 37. This gives the units and tens digits of the result. Since
24 < 87, we have actually subtracted 87 from 124 i.e. we have
borrowed 1 from 8 ( of 824). So, we now do (7-5) = 2. The result is 237.
(For
new learners, this technique may look lil confusing. If you feel it is
confusing, then just read it for two times and try to understand the
logic behind it).
- Adding 100s complement of 58 (which is 42, i mean 58 + 42 = 100) to 17, we get (42+17) = 59 which gives the units and 10s digits of the result.
- Since
58 is greater than 17, we have to borrow 1 from 92 which leaves us with
91. So, the first part of the answer is 91 - 8 = 83. SO, the result is
8359.
- 934 - 286 + 847 - 798 = ?
- When
we have a combination of additions and subtractions, first add all the
numbers with + sign before them and add all the numbers with - sign
before them.
- I mean (934 + 847) - (286 + 798) = 1781 - 1084
- By applying the method explained in previous examples, 1781 - 1084 = 697.
