The sea ice around the south pole fluctuates between 18 million square kilometers in September to 3 million square kilometers in March. During how many months are there more than 15 million square kilometers of sea ice?

Answer 1

Assuming a sinusoidal function, we have the area is (letting x=0 in September)

a(x) = 7.5 cos(pi/6 x) + 10.5
we want a(x) > 15. In other words,

cos(pi/6 x) > 0.6

-1.77 < x < 1.77 so, using symmetry, in one complete period (a year), there are 3.54 months with more than 15 Mmi^2 of ice