Question

a five digit no is formed using the digits 1,3,5,7,9 without repeating any of them.what is the sum of all such possible five digit nos?

Answer 1

how many such numbers are there?

Answer 2

they will be 120

Answer 3

of the 120 how many times will the 1 be in the ten thousands place?

Answer 4

probably 24

Answer 5

yes exactly 24

Answer 6

otherwise some other number would be there more !

Answer 7

similarly the 3 will be there 24 times
the 5 and 7 and 9 also

Answer 8

yea therefore there sum would be 24(1+3+5+7+9)

Answer 9

yes, for each place

Answer 10

for the ten thousands place it would be
\[10,000\times 24\times (1+3+5+7+9)\]

Answer 11

better known as
\[10,000\times 24\times 25\]
repeat for each place

Answer 12

got it thnx

Answer 13

yw

Answer 14

use symmetry..
\[\Large\frac{97531+13579}{2}\cdot 5!\]

Answer 15

ooh much slicker

Answer 16

not sure i would ever have come up with adding forwards and backwards