numpy got installed in Python3.5 but not in Python3.6
Cannot comment since I don't the rep. 
If your default python is 3.5 when you check python --version, the way to go would be to find the location of the python executable for the desired version (here 3.6).
cd to that folder and then run the command given by Mike.
I have both Python 3.5 and Python 3.6 on my laptop. I am using Ubuntu 16.04. I used pip3 to install numpy. It is working with Python3.5 but not with Python3.6. Please help.