When Creating a new Angular 5 project:
node version: 8.9.2
npm version: 5.5.1
My Command is
npm install -g @angular/cli
This command alone solved my problem:
npm cache clean --force
Also you should make sure you are using the correct version of node.
Using nvm to manage the node version:
nvm list; # check your local versions;
nvm install 10.10.0; # install a new remote version;
nvm alias default 10.10.0; # set the 10.10.0 as the default node version, but you have to restart the terminal to make it take effect;