Stage: 4 Challenge Level: 
Brian swims at twice the speed that the river is flowing. He swims directly downstream, from one moored boat to another and back again, taking 12 minutes altogether. How long would it have taken him in still water?
engineering. Short problems. Manipulating algebraic expressions/formulae. Factorisation (algebraic). Stage 5 needs dealing with. Speed. Stage 5 - Reviewed 2012. Forces. Polynomials. Mathematical reasoning & proof.
Published February 1997.
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