Installing Octave in Ubuntu running on Docker

I want to run Octave on Ubuntu running on docker.  Simple stuff but still manage to get errors and had to spend  few minutes on fine-tuning 

Here it goes

1- Start docket and get Ubuntu image from repo

    - Couple of commands

            - docker pull ubuntu

            - docker run -it ubuntu 

2- Install Octave 

    - ran command "apt-get install octave" and here it goes error "Unable to locate package Octave"

  

3- to come over this issue run below commands

    - apt-get update

    - apt-get install octave 

Done......