The binary number 11001 in the decimal number system is equal to:

= $1 \times 2^4 + 1\times 2^3 + 0\times 2^2 + 0\times 2^1 + 1\times 2^0$

$1\times 2^4 = 1\times 16 =16$
$1\times 2^3 = 1\times 8 = 8$
$0\times 2^2 = 0 \times 4 =0$
$0\times 2^1 = 0\times 2= 0 $
$1\times 2^0 = 1\times 2 =1$
now total
16 + 8 + 0 + 0 + 1 = 25
Answer = 25