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^22. 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)...

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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