Two 10 kg bodies are attached to a spring balance as shown in figure. The reading of the balance will be

Two 10kg bodies are attached to the spring balance as shown.

Let the bodies are in equilibrium i.e. $a=0$  

Then we can have T = 10kg wt

We know when force is applied on a spring then its stretches and transfer

the same force to the other end.

$\therefore$  We get spring force is also equal to = T.

Hence reading of spring balance T = 10kg wt.