If you want to close a bunch of apps all at once, open the App Switcher and use multiple fingers to drag up the app icons.
Close multiple apps at once in the App Switcher
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Fix a typo in the iPhone Calculator app
Swipe left or right on the numbers to delete the last digit without clearing your equation.
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8 Useful iPhone Features and Tips You Should Try
Helpful iPhone features including sleep timer, measure app, music volume boost, and location shortcuts