Total Number of socks = 4 pairs= 8 socks
Number of red socks = 4
Number of black socks = 4
Probability of pulling a red sock from the bag the first time =

Since the sock is placed back in the bag before pulling a sock again, the number of socks remains the same.
So,
Probability of pulling a red sock from the bag the second time =

And
Probability of pulling a red sock from the bag the third time =
Therefore, the probability of pulling a red sock 3 times from the bag =
