Solution:
Given that;
There are 6 nickels and 7 dimes in your pocket.
Let N represent nickels and D represent dimes
Total coins will be
You randomly pick a coin out of your pocket and then return it to your pocket.
The probability of picking a nickel is
Since the coin was returned, the total number of coins is still the same
Then, you randomly pick another coin.
The probability of you picking a nickel both times will be
Hence, the answer is 36/169