Assume that the wavelengths of photosynthetically active radiations (PAR) are uniformly distributed at integer nanometers in the red spectrum from 640 to 680 nm. What is the mean and variance of the wavelength distribution for this radiation?

Renewable Energy Division–CIEMAT, 28040 Madrid, Spain
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E.T.S.I. Agronómica, Alimentaria y de Biosistemas, Universidad Politécnica de Madrid, 28040 Madrid, Spain
3
CRETUS Institute, Department of Chemical Engineering, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain
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I’m pretty sure the answer is a