Create a /etc/yum.repos.d/mongodb-org-4.0.repo

Install MongoDB Community Edition on Red Hat Enterprise or CentOS Linux — MongoDB Manual https://docs.mongodb.com/manual/tutorial/install-mongodb-on-red-hat/

Configure the package management system (yum).

Create a /etc/yum.repos.d/mongodb-org-4.0.repo file so that you can install MongoDB directly using yum:

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[mongodb-org-4.0]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/4.0/x86_64/
gpgcheck=1
enabled=1
gpgkey=https://www.mongodb.org/static/pgp/server-4.0.asc