Explanation for Question 4 From the Math (Calc) Section on the 2020 October Sat
So question number four asks us about the desert region and it wants to 2 know which of the following could be the amount of light reflected 3 from the one meter square surface. 4 And so if we look back up at our question, we'll see, 5 it gives us a definition for albedo. It says the albedo is the amount 6 of light reflected, divided by the amount of light falling on the surface. 7 So we can write that as an equation, a albido is the amount of 8 light reflected versus the amount of light falling on the surface and 9 in this equation or in this question, actually it tells us that the amount 10 of light falling on the surface from the sun is 1000 Watts. 11 So a is equal to something over 1000, 12 and this is what we're looking for. Right? We're searching for reflected. 13 That's what it's asked us for. And so we can ask ourselves what is 14 a about in the desert region. 15 It gives us a range. If we look at the desert region, 16 these are pretty close together, right? So maybe we pick a number in between 17 for RA. We could say about two point or 0.28, 18 cause that's in between two points, 0.2, six, 19 and 0.29. And so now the self are for our, 20 remember this is a calculator question. So you can just do 0.2, 21 eight times 1000. You can use a calculator or your head, 22 and you can see that we get are as equal to two 80. 23 And the one that's closest to two 80 is a and a is the 24 right answer. Even though it's not exactly two 80, 25 we know that we just had to pick a number somewhere within this range. 26 And so 0.28 is close within the range. 27 Everything else is way too far away to be within that range. 28 And so our correct answer is going to be a.