Q1.

Do you know how to plot the graph of 5cos((pi)t/2) + 5 ? You'll probably have to know about basic graph transformations to do so. If you're not sure about these, this is pretty useful, it explains all the basic rules: New Functions from Old

And here's what it looks like:

http://i121.photobucket.com/albums/o...g?t=1240259802

So the lowest productivity is where the graph has the lowest value. On here it's where the graph hits zero. Go along the x-axis counting up the hours, starting with 8am at 0, and you'll find 10am and 2pm are your answers