Since 10 ohm, 20 ohm and 50 ohm are in parallel so resistance will be

1/R_p = 1/10 + 1/20 + 1/50

R_p = 100/17

Then 10 ohm is in series

So effective resistance = 100/17 + 10 which will be more than 10 ohm but less than 20 ohm.