Answer Within A Minute III

Algebra Level 1

$\frac{1}{3} \times \frac{3}{5} \times \frac{5}{7} \times \frac{7}{9} \times \frac{9}{11} \times \cdots \times \frac{47}{49}$

If the value of the expression above equals $\frac ab$ for coprime positive integers $a$ and $b$ , find the value of $a+b$ .