Find the next numbrr 3,8,15,24,35,?

$8 - 3 = 5$
$15 - 8 = 7$
$24 - 15 = 9$
$35 - 24 = 11$

The differences are 5, 7, 9, 11. This is an arithmetic progression where each term increases by 2.

The next difference will be $11 + 2 = 13$.

Add the next difference to the last term: $35 + 13 = 48$.

Alternatively, observe the pattern as one less than a perfect square:
$2^2 - 1 = 3$
$3^2 - 1 = 8$
$4^2 - 1 = 15$
$5^2 - 1 = 24$
$6^2 - 1 = 35$
So, the next number would be $7^2 - 1 = 49 - 1 = 48$.

The next number is 48.