Calculations - Quant/Math - CAT 2013
Question 4 the day:
June 14, 2002
Here is the second tip for calculating fast. The first tip was sent on June 4, 2002.
If you have a pair of numbers like 22 and 28 and you need to multiply the two of them.
This rule applies to numbers whose units digits add up to ten (2 and 8 in this case) and the tenth digits are same.
Step 1:
Multiply the unit digits
2 * 8 = 16
Step 2:
Increment the tenth digit by 1.
2 + 1 = 3
Step 3:
Multiply the incremented number with the original tenth digit number
3 * 2 = 6
Step 4:
Concatenate the results got from step 1 and step 3
6 and 16 => 616
Note: Remember to put the products of unit digits of the given numbers in the unit and tenth digit of your result.
Example 2: 36 * 34 = ?
Step 1:
Multiply the unit digits
6 * 4 = 24
Step 2:
Increment the tenth digit by 1.
3 + 1 = 4
Step 3:
Multiply the incremented number with the original tenth digit number
4 * 3 = 12
Step 4:
Concatenate the results got from step 1 and step 3
12 and 24 => 1224
Therefore, 36 * 34 = 1224
Example 3: 61 * 69 = ?
Step 1:
Multiply the unit digits
1 * 9 = 9. In this case remember to write 9 as 09
Step 2:
Increment the tenth digit by 1.
6 + 1 = 7
Step 3:
Multiply the incremented number with the original tenth digit number
6 * 7 = 42
Step 4:
Concatenate the results got from step 1 and step 3
42 and 09 => 4209 (Since, we have to put the product of the unit digits only in the unit and tenth digit of the result)
Therefore, 61 * 69 = 4209
Example 4: 127 * 123 = ?
Step 1:
Multiply the unit digits
7 * 3 = 21
Step 2:
Increment the tenth digit by 1.
12 + 1 = 13
Step 3:
Multiply the incremented number with the original tenth digit number
12 * 13 = 156
Step 4:
Concatenate the results got from step 1 and step 3
156 and 21 => 15621
Therefore, 127 * 123 = 15621
Try out the above technique with the following problems.
Questions
- 54 * 56
- 79 * 71
- 152 * 158
- 33 * 37
- 111 * 119
- 3024
- 5609
- 24016
- 1221
- 13209
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