Question: I'm a beginner for Angular.I'm using the latest Angular version (Angular: 9.1.11) and tried to install bootstrap by the command,
`ng add @ng-bootstrap/schematics`
Though it gave the message that Packages installed successfully Suddenly the compilation fails and gives the error 

```
Failed to compile.

src/app/app.module.ts:9:27 - error TS2307: Cannot find module '@ng-bootstrap/ng-bootstrap'.

9 import { NgbModule } from '@ng-bootstrap/ng-bootstrap'

```

So I thought that it is a bootstrap installation error and ran the command 
`ng add @ng-bootstrap/schematics` again 

Now the case has become worse.Now the Angular server doesn't start and it shows 

```
An unhandled exception occurred: Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema.
 - configuration.entry['styles'] should not contain the item 'E:\AngularProject\DreamsApp\node_modules\bootstrap\dist\css\bootstrap.css' twice.
   -> A non-empty array of non-empty strings
See "C:\Users\Sam\AppData\Local\Temp\ng-iHB2eT\angular-errors.log" for further details.

```

The error contains `should not contain the item ___ twice` part I think that is because I ran the `ng add @ng-bootstrap/schematics` command twice.

So I want to know that whether running twice that command is a problem in Angular???.And please give me a Solution for this to correct.Thankyou!!

Answer: 
you can simply install bootstrap using 
`npm install bootstrap --save`

and then you can include bootstrap js and css file in angular.json like below:

```
"styles": [
              "node_modules/bootstrap/dist/css/bootstrap.min.css",
              "src/styles.scss"
            ],
"scripts": ["node_modules/bootstrap/dist/js/bootstrap.min.js"]

```
Let's uninstall and install it again.

1- Go to `angular.json` and remove:

```
"node_modules/bootstrap/dist/css/bootstrap.min.css"

```

2- Go to package.json and remove the package from there

3- Go to `node_modules` and delete `bootstrap` directory

Kill the running process and run it again `ng serve`.

And install the package again:
`ng add @ng-bootstrap/ng-bootstrap`