Mathematical formulae and principles Flashcards
1
Q
Divisibility by 7?
A
No. of tens in the no.- [Units digit*2] should be divisible by 7.
Over and over again till u get to a comfortable no.
2
Q
Divisibility By 19
A
No. of tens + 2(Units digit) should be divisible by 19.
[over and over again]
3
Q
Sum of all the factors of a number
such that N= a^p . b^q . c^r
A
(a^(p+1) - 1)(b^(q+1) -1)(c^(r+1) - 1)/(a-1)(b-1)(c-1)
4
Q
A
5
Q
No. of ways of writing a no as a product of two coprimes
n=a^x.b^y.c^z
A
2^(Q-1)
where q is the no. of cistinct prime components or factors
