Unable to locate package openssl-dev

I'm trying to install the ROOT CERN packages on linux, using Ubuntu 18.04, and whenever I get into the prerequisites download, with this command:

sudo apt-get install dpkg-dev cmake g++ gcc binutils libx11-dev libxpm-dev libxft-dev libxext-dev python openssl-dev

I get the following output:

Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package openssl-dev

I've tried correcting this by configurating my repository as was suggested in this thread, yet the problem still persisted.

Would like to know how is it possible to fix this. Thank you.

Edit:

The complete output of the sudo apt update command is:

Hit:1 bionic InRelease
Hit:2 bionic-security InRelease
Hit:3 bionic-updates InRelease
Reading package lists... Done
Building dependency tree
Reading state information... Done
All packages are up to date.

I've also tried installing the libssl-dev package with sudo apt install libssl1.0-dev and the outcome remains unchanged.

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