Free Tips to do Mental Arithmetic Questions Easy in 2011- Part 5
This is my fifth blog of tricks to do well in math problems. Please find some good tips to do math questions easy. These tricks are easy to remember to do all math calculations:
31. Math: 9X Rule
To multiply by 9, try this:
(1) Spread your two hands out and place them on a desk or table in front of you.
(2) To multiply by 3, fold down the 3rd finger from the left. To multiply by 4, it would be the 4th finger and so on.
(3) The answer is 27 ... READ it from the two fingers on the left of the folded down finger and the 7 fingers on the right of it.
This works for anything up to 9x10!
32. Easy Division by 5
Often, instead of dividing by 5, it is more convenient to multiply first by 2 and then divide the result by 10. For example,
Step 1 multiply first by 2
Step 2- divides the result by 10
1375/5 = 2750/10 = 275.
7205/5 = 14410/10 = 1441.
33. Easy Addition of 5
When adding 5 to a digit greater than 5, it is easier to first subtract 5 and then add 10.
For example,
Step 1- first subtract 5
Step 2- then add 10.
7 + 5 = 12.
Also 7 - 5 = 2; 2 + 10 = 12.
35 Easy Multiplications by 8
Replace either with a repeated operation by 2.
For example,
124×8 = 248×4 = 496×2 = 992.
36. Easy subtraction.
Subtraction is often faster in two steps instead of one.
For example,
A generic advice might be given as "First remove what's easy, next whatever remains".
1049 - 187 = 1000 - (187 - 49) = 900 - 38 = 862.
37. Easy addition.
Addition is often faster in two steps instead of one.
For example,
487 + 38 = (487 + 13) + (38 - 13) = 500 + 25 = 525.
A generic advice might be given as "First add what's easy, next whatever remains". Another example:
1049 + 187 = 1100 + (187 - 51) = 1200 + 36 = 1236
another good tricks to do well in math is remember all tables both backwards and forwards
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