Tollbooth truth!

There was a blonde, a brunette, and a red head. They were on a road with a tollbooth. At the tollbooth, instead of having to pay to get on the road, they had to state a fact. If they told a lie, the ground would open up and swallow them. The brunette went first, when she got to the tollbooth, she said, "I think red and blue mixed makes purple." she walked onto the road without the ground opening up and swallowing her. The redhead went next. When she got to the tollbooth, she said "I think 2+2 is 4." she walked onto the road without the ground opening up and swallowing her. The blonde went last. When she got to the tollbooth, she said "I think" and the ground opened up and swallowed her.