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Some shortcuts of math

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Joined: 27 Jul 2011
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Some shortcuts of math [#permalink]

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New post 17 Aug 2012, 18:45
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This set is mixed one:(it is always good to approach formal way rather than to put some shortcut formulas....But why not give a try if it can save some time )

1. Area of a circle circumscribing equilateral triangle = \(\frac{pi}{3}a^2\)

2. Area of a circle inscribed in a equilateral triangle= \(\frac{pi}{12}a^2\)

3. Triangle formed by joining the mid points of a equilateral triangle will be half of perimeter and \(\frac{1}{4}area\).

4.For a infinite GP series sum = \(\frac{a1}{(1-r)}\) where a1 is the first term and r is multiplication factor

5. When Difference between compound interest and simple interest on a certain sum of money for 2 years at r% is
= \(\frac{(DIffX 100X100)}{(RateXRate)}\)

6. WHEN diff between CI and SI for 3 years at r% is given , then sum = \(\frac{Diff X100X100X100}{{(r^2)X(300+r)}}\)

7. If sum A becomes sum B in t1 years at compound rate of interest , then after t2 years the sum becomes

I am having a headache writing it properly - it is \({B^(t2/t1)} / { A^{(t2/t1)-1}}\)

8. Certain distance covered in xkm/hr and same distance y km/hr then avg speed = \(\frac{2xy}{x+y}\)

9. If two persons A and B start at the same time in opposite directions from two points and after passing each other they complete the journey
in a hrs and b hrs respectively . then A's speed : B's Speed = \(\sqrt{b} : \sqrt{a}\)

10.A man takes x hours to walk a certain place and ride back. However if he walks both ways he needs t hours more . Thus time taken
by him to ride both ways = \((x-t)\) hours.

I will post other tips if u like my post...(I mean If get few few kudos)...

If u can't jump the 700 wall , drill a big hole and cross it .. I can and I WILL DO IT ...need some encouragement and inspirations from U ALL

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Re: Some shortcuts of math [#permalink]

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New post 27 Aug 2012, 09:01
Good initiative but honestly you are better off understanding concepts than memorizing "non-standard" abstruse formulae. Many high-performing quant students tend to rely on understanding quant through basic first principles. Moreover, higher level (700+) questions on the GMAT are so based on simple math and flexibility in thinking that sometimes memorized formulas can be a handicap, as they tend to restrict your thinking and frustrate you when you realize that you can't simply plug and chug.

That said, I understand different test takers use different strategies, so to each his own.

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Re: Some shortcuts of math [#permalink]

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New post 28 Aug 2012, 18:10
Personally, I agree with OldFritz, it is absolutely unnecessary to burden one's brain with abstruse formulas. For example, I am pretty certain that a very very small subsection of 99% scorers would know the expression for the Area of a circle circumscribing equilateral triangle. The GMAT doesn't really emphasize that. The only formula that I have ever used on the GMAT is the expression for the area of an equilateral triangle with side s, [sqrt(3)*s^2]/4. Other than that a problem solving mind set, along with the ability to think and approach a problem in multiple ways is probably more relevant for the GMAT.

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Re: Some shortcuts of math [#permalink]

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New post 10 Sep 2012, 14:14
Though memorizing a few formula are helpful in quickly answering, however memorizing complicated formulas is sometimes difficult, specially geometry related formulas.

For your first two formulas, I would prefer to derive this value from properties of triangle ( Heitht = \(\sqrt{3}* a/ 2\)) , instead of memorizing them.

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Re: Some shortcuts of math [#permalink]

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New post 09 Mar 2017, 08:15
Some of the more GMAT-specific shortcuts are in my guide here: ... -shortcuts

Properties of Numbers concepts and shortcuts here: ... -questions

Fractions shortcuts here: ... gymnastics

Learn the Top 3 GMAT Arithmetic Techniques with this free PDF guide!

Re: Some shortcuts of math   [#permalink] 09 Mar 2017, 08:15
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Some shortcuts of math

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