Are these sentences incorrect?

[letsglow]

1. "Mary spread butter all over her piece of toast with her knife"

2. "When the baloon burst everyone was startled by the sudden noise"

[josef]

I'd say that given a full stop and with balloon spelled correctly neither sentence is incorrect. My only slight hesitation is that it might be more natural to say: "Mary spread butter all over her toast with her knife." But if in the context it's important to specify "piece of toast" then that's natural too, and in no case "incorrect".

[xiphiasatsi]

Hello,

I can help you with the second sentence.The correct sentence is-

"When the baloon burst, everyone were startled by the sudden noise"

[Joe]

The correct sentence is-
"When the baloon burst, everyone were startled by the sudden noise"

Not quite...

The correct spelling is "balloon".

And everyone is singular: "everyone was startled"