Mathematics Tips and Tricks

Example 1 : Finding Square of a number ending with 5


To find the square of 75
Do the following
Multiply 5 by 5 and put 25 as your right part of answer.
Multiply 7 with the next higher digit ie (7+1)=8 gives
56 as the left part of the answer, Answer is 5625


Example 2 : Calculate 43 X 47



The answer is 2021 Same theory worked here too.
The above 'rule' works when you multiply 2 numbers with units digits add up
to 10 and tenth place same


Example 3: Multiply 52 X 11



Answer is 572
Write down the number being multiplied and put the total of the digits between 2 digits
52 X 11 is [ 5 and 5+2=7 and 2 ] , answer is 572


Example. 4: Find 994 X 988.



Here base is 1000
994 -006 [ BASE 1000]
988 -012
-------------------
(786-002) or (998-214) / (214X2)
994 -006 [ BASE 1000]
988 -012
-------------------
982 / 072
Answer is 982072


Example.5: Find 13X12.



Base is 10
13 3 [ BASE 10]
12 2
-------------------
(13 + 2) or (12 + 3) / (3 X 2)
13 3 [ BASE 10]
12 2
-------------------
15 / 6
Answer is 156

Example 6: Find 15 x 99



• Step 1: 15 - 1 = 14
• Step 2: 99 - 14 = 85 (or Complement of 15 , 100 -
15)
• Step 3: 15 x 99 = Answer is 1485


Example 7: Multiply 42 by 13



Step 1. Starting from left, multiply the two left
handed most digits vertically. 4 X 1 = 4 and
set the answer down underneath as the left
most part of the answer.
4 2 X
1 3
---------
4
Step 2. Multiply 4 by 3 and 2 by 1, cross
multiplying and add these two answers
together 4 X 3 + 2 X 1 = 14. Set down 4 as the
next answer digit and carry the 1 to the left.
4 2 X
1 3
---------
4 14
Step 3. Multiply 2 by 3 vertically and set down
the answer 6 as the right most answer digit.
4 2 X
1 3
----------
4 14 6
Step 4. Add to the carry digit to give the
answer 546
This method can be started either from the right or from
the left.