Here’s a collection of time-saving math shortcuts, great for back-of-the-envelope estimates
Shortcut to multiplication
Square Number
Tips 1: 2 Digit Number which ends in 5
Step1: Multiply the first digit of number, with the next to its number. Ex: 45 is the number you want to square. 4 x 5 = 20
Step2: Finally add 25 at the end of the result.
Answer=2025
Step1: Multiply the first digit of number, with the next to its number. Ex: 45 is the number you want to square. 4 x 5 = 20
Step2: Finally add 25 at the end of the result.
Answer=2025
Tips 2: Any 2 Digit Number
Ex: 47
Step1: Look for the nearest 10 boundary.
3 from 47 to 50
Step2: Since we went up 3 to 50, now go down 3 from 47 to 44.
Step3: Now mentally multiply 44 x 50 = 2200 - 1st answer.
Step4: 47 is 3 away from the 10 boundary 50, Square 3 as 9 - 2nd answer.
Step5: Add the first and second answer, 2200 + 9
Answer: 2209
Source: http://www.helpwithassignment.com/
Ex: 47
Step1: Look for the nearest 10 boundary.
3 from 47 to 50
Step2: Since we went up 3 to 50, now go down 3 from 47 to 44.
Step3: Now mentally multiply 44 x 50 = 2200 - 1st answer.
Step4: 47 is 3 away from the 10 boundary 50, Square 3 as 9 - 2nd answer.
Step5: Add the first and second answer, 2200 + 9
Answer: 2209
Source: http://www.helpwithassignment.com/
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