Answer:
The number Bishwant thought of is 4.
Explanation:
First, let's think about what we can eliminate.
If Bishwant doubled the number and added 5, getting 13--then the number he thought of is obviously less than 13, 12, 11, 10, 9, 8, and 7.
Now, let's do some trials!
6 + 6 = 12; 12 + 5 = 17 <-- Incorrect
5 + 5 = 10; 10 + 5 = 15 <-- Incorrect
4 + 4 = 8; 8 + 5 = 13 <--Ah!
4 is the answer! (If you have any questions about this riddle, feel free to comment--but, please stay respectful everywhere, all the time.)