You're at a restaurant with your kids. You are all looking at the menu and trying to decide what to get. Everyone has decided except for your daughter. The waiter is coming over to your table, so you want her to decide quickly. You tell her this.
Hurry up and make up your mind.
This means to do something quickly. "Hurry up and ___" is used in casual situations, and usually when you are a little frustrated with how long someone is taking to do something.
The phrase "make up your mind" means to decide. It's usually used when someone is considering a few different choices and can't decide which of the choices to go with.
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