# From project directory:
npm install --save bootstrap
npm install --save jquery

# Now edit `angular.json`
# Position: `projects -> architect -> build -> options`
# To `styles`, add "node_modules/bootstrap/dist/css/bootstrap.css"
# To `scripts`,
#   add "node_modules/jquery/dist/jquery.js"
#   and also "node_modules/bootstrap/dist/js/bootstrap.js"
# Test with
# <<div class="alert alert-primary" role="alert"> Bootstrap alert</div>

@import "~bootstrap/dist/css/bootstrap.css"

 "styles": [
              "./node_modules/bootstrap/dist/css/bootstrap.css",
              "src/styles.css"              
            ],

From angular cli:

npm install --save bootstrap
npm install --save jquery

Then add the following paths to angular.json:

"node_modules/bootstrap/dist/css/bootstrap.css" in the projects -> architect -> build -> styles array
"node_modules/jquery/dist/jquery.js" in the projects -> architect -> build -> scripts array
"node_modules/bootstrap/dist/js/bootstrap.js" in the projects -> architect -> build -> scripts array

npm install --save bootstrap

npm install bootstrap

"styles": [
  "node_modules/bootstrap/dist/css/bootstrap.min.css",
  "styles.scss"
]