Maths tricks and short cuts for exams Bank PO, SSC, Clerical, Insurance, CSAT, others

MATHEMATICS FUNDAE FOR CLERICAL, BANK PO, SSC EXAMS AND OTHERS EXAMS


 

To find the number of factors of a given number, express the number as a product of powers of prime numbers.

Take the example of 576.          576 = 64*9 = 26 x 32
It is like 20, 21, 22, 23, 24, 25, 26   X   30, 31, 32
To get No. Of factors what is there is that you take any thing from 2's power multiply by anthing from 3's power, that will divide your initial number because it has that many  number of 2's and 3's . Right. So how many combination are possible ? On left are 7 and right are 3 so net will be 7 x 3 =21 factors.

In other words just remember
After finding that 26 x 32 step, just do (6+1) x (2+1) = 7 x 3 =21 factors.

Note - If question ask you not to count 1 & 576 as factors, then subtract 2 from answer means 21-2=19. Otherwise don't subtract unnecessarily.

The sum of first n natural numbers = n (n+1)/2

Eg The sum of 1+2+3+……..+10+11+12 = ??

Here n = 12 so Sum     = 12 ( 12+1 ) / 2
                                    = 12 * 13 /2 = 6 * 13 = 78



The sum of squares of first n natural numbers is   n (n+1)(2n+1)/6

Eg the sum of 12 + 22 + 32 + 42 + ………. +122 =??

                        = 12 (12+1) (2*12 + 1) /6
                        = 12*13*25 /6 = 650




The sum of first n even numbers= n (n+1)

Eg The sum of 2+4+6+8+10+…………. +40 = ??
            Here n ≠40. N is the no of terms. So number of terms here is 20, the value of 20th term is 40 indeed. So with n = 20

                        Sum = 20 (20+1) =20*21 =420



The sum of first n odd numbers= n2

Eg The sum of 1+3+5+7+9+11+…………..+21

Here n≠21. Here number of terms are 11 so n=11.
                        Sum = 112 = 121





To find the squares of numbers near numbers of which squares are known
For eg you might know squares of 20,30,40,.. Very easily.
So
To find square of 41 which is near to 40, Add 40+41 to 1600 =1681

To find 592 , which is near to 60, Subtract 602  - (60+59)  =3600-119 = 3481
                                   
Add when the number is more and subtract when the number is less.
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योग इकाई हो गुरु दहाई, 
एक समान हो गिनती बाँयीं ।
एक दहाई में जोड़ो एक, 
गुणा करो और दे दो फेंक ॥

उदाहरण 1- 34 को 36 से गुणा करने के लिए किसी एक दहाई में एक जोड़कर यानी 3+1 = 4x3=12 व इकाई का गुणा इकाई से गुणा यानी 4x6=24 होगा। दोनों संख्यायें बराबर लिखने पर उत्तर प्राप्त हो जायेगा: 1224 (देखें चित्र)
उदाहरण 2- 413 X 487
413 X 487
= 4 x 5 / 13 x 87 (एक दहाई में एक जोड़ा )
= 20 /1131 (दहाई X दहाई/ इकाई X इकाई)

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Nice and easiy trick

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