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Not all scientists are smashing particles, discovering new chemicals or exploring exotic environments. Some scientists strive to keep things working in your home. It takes a lot of science to test everyday objects, such as toilets, to make sure they work the way they should.

Fred’s teacher has a weird way of marking tests. He gives five marks for a right answer, but subtracts one for a wrong one. Fred answered 20 questions on a test and got 70 marks. How many questions did Fred get right?