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Rapid Math

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Manager
Status: Enjoying the Journey
Affiliations: ND
Joined: 26 Sep 2017
Posts: 114
Schools: Rotman '21
WE: Marketing (Consulting)

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Updated on: 12 Nov 2017, 04:48
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Hi Everyone,

Although GMAT doesn't test your ability to perform complicated calculations, it would be beneficial to know some calculation tricks that would save you some time.

Trick 7: Rapidly Square Any Number Ending in 5

Multiply the tens digit by the next whole number then affix the number 25
$$65^2: 6*7=42 ==> 'affix' 25 ==> 4225$$

Trick 8: Rapidly Multiply Any Two-Digit Number by 11

Write the number leaving some space between the two digits, then insert the sum of the number's two digit in between.

24*11 ==> 2 ? 4 ==> 2+4=6 ==> 264

Trick 9: Rapidly Multiply by 25 (or 0.25, 2.5, 250, etc.)

Divide the number by 4 and affix or insert Zeroes or decimal points
Example: 28*25 ==> 28/4 = 7 ==> 700 (add 2 Zeroes)

Trick 10: Rapidly Divide by 25 (or 0.25, 2.5, 250, etc.)

Remove Zeroes or decimal points then multiply the number by 4
Example: 700/25 ==> 7/25 ==> 7*4=28

Trick 24: Rapidly Square Any Two-Digit Number ending in 1

$$21^2 ==> 20^2=400 ==> Add: 20+21=41 ==> Add: 400+41= 441 ==> 21^2 = 441$$

Trick 59: Rapidly Multiply Any Three-Digit Number by 11 (advanced variation of trick 8)

Write the number leaving some space between the two digits, then insert the summations of the numbers in between (summations of 2 digits everytime; as shown below).

Example:

342*11=??
342*11= 3--2 (write the first & the last number "3"& "2")
342*11=3-62 (the sum of 4+2)
342*11=3762 (the sum of 3+4)

Source: Rapid Math Tricks & Tips. EDWARD H. JULIUS
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GMAT Club Live: 5 Principles for Fast Math: https://gmatclub.com/forum/gmat-club-live-5-principles-for-fast-math-251028.html#p1940045
The Best SC strategies - Amazing 4 videos by Veritas: https://gmatclub.com/forum/the-best-sc-strategies-amazing-4-videos-by-veritas-250377.html#p1934575

Originally posted by NDND on 23 Oct 2017, 01:32.
Last edited by NDND on 12 Nov 2017, 04:48, edited 5 times in total.
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Joined: 07 May 2017
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Location: Indonesia
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23 Oct 2017, 01:47
Thanx. It will help

Sent from my Redmi Note 3 using GMAT Club Forum mobile app
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Manager
Status: Enjoying the Journey
Affiliations: ND
Joined: 26 Sep 2017
Posts: 114
Schools: Rotman '21
WE: Marketing (Consulting)

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01 Nov 2017, 07:43
Updated with Tricks 9 & 10
_________________

"it takes more time to fix a mistake than to avoid one"
"Giving kudos" is a decent way to say "Thanks" and motivate contributors. Please use them, it won't cost you anything

High achievement always takes place in the framework of high expectation Charles Kettering
If we chase perfection we can catch excellence Vince Lombardi

GMAT Club Live: 5 Principles for Fast Math: https://gmatclub.com/forum/gmat-club-live-5-principles-for-fast-math-251028.html#p1940045
The Best SC strategies - Amazing 4 videos by Veritas: https://gmatclub.com/forum/the-best-sc-strategies-amazing-4-videos-by-veritas-250377.html#p1934575

Re: Rapid Math &nbs [#permalink] 01 Nov 2017, 07:43
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