Q:

how to install numpy for already installed python 3.8.1 on ubuntu 18.04

I have three versions of python 2.7 , 3.6 and 3.8.
I installed "numpy" on 3.8 many times but does not work on jupyter notebook.
Any thing will be great help because i have a task to submit tonight
linux commands 
> sudo apt update
> sudo -H pip3 install --upgrade pip
> sudo -H pip3 install virtualenv
> mkdir ~/my_project_dir
> cd ~/my_project_dir

and here i ran a single command to install jupyter notebook , which i forgot but it was suggested to me by the terminal

A:

I agree with @8hubham - download and install anaconda from here. 
Then in your terminal, you can create a virtual environment where you can choose your specific version of python (3.8):
conda create --name myenv python=3.8

Then activate the virtual environment:
conda activate myenv

You can pip install numpy now:
pip install numpy

Now with pip install ipykernel and jupyter:
pip install ipykernel
pip install jupyter

Finally, install a kernel for your virtual env:
python -m ipykernel install --user --name myenv

When you launch a Jupyter notebook server from your terminal within the virtual environment you just set up ("myenv"), you should see your myenvkernel in the drop-down menu when setting up a new notebook:
jupyter notebook server new notebook with myenv kernel:

