Question

FIND THE SUM OF NATURAL NUMBERS LESS THAN 100 WHICH ARE DIVISIBLE BY 5 OR 7.

Answer 1

Heya User,

--> Divisible by 5 / 7 ... Ummm. √√

We find the individual sum of all such no.s divisible by '5' and then '7' and add them up >_< ...

--> First -->[ 5 x 1 ]+[ 5 x 2 ]+...[ 5 * 19 ] ->{ since, no.s are less than 100 }

-->   = [ 5 ] [ 1 + 2 + ... + 19 ] = 5 [ 190 ] = 950 √√  --> ( i )

Now, similarly

------> [ 7 x 1 ] + [ 7 x 2 ] + ... + [ 7 x 14 ] √√

---> [ 7 ] [ 1 + 2 + .. + 14 ] = [ 7 ][ 105 ] = 735 √√   --> ( ii )


Now, I add both ( i ) and ( ii ) and we're done -->

---> THE SUM OF NATURAL NUMBERS LESS THAN 100 WHICH ARE DIVISIBLE BY 5 OR 7  ---> [ 735 ] + [ 950 ] = 1685 √√