Explanation for Question 26 From the Math (Calc) Section on the 2020 October Sat
So question number six gives us a situation about an airplane and how much 2 fuel it uses as it flies. And it asks us to come up with 3 an equation for it. And this is really a unit analysis question, 4 because what we need to do here is we need to think about what 5 numbers do we need to put together to create a unit here that will 6 allow this part of our equation, the second part to be gallons. 7 And now the reason that second part of our equation needs to be gallons 8 is because the answer that we want is in gallons and the other number 9 in the equation is gallons. So our ultimate goal is to try to change 10 this one here so that we can go from working in hours to 11 working in gallons and now to get from hours to gallons, 12 I need the hours to cancel, right? 13 So I would put need something with hours on the bottom, 14 and then I would need a gallons on the top because if whatever 15 I had in parentheses was like that I could cancel out my hours and 16 I'd be left with gallons. So that means that what I want to create 17 here is something and units of gallons per hour. 18 And I know that I started with, 19 um, where I started with the 600,000 gallons, 20 but I'm going at a speed of 550 miles 21 per hour, right? So there's the hours that I wanted in my denominator. 22 I can get it from there. And now I got to figure out how 23 do I get gallons into the equation? And I could see the earlier in 24 the equation, I have five gallons per mile. 25 So now if I do five gallons per mile, if I multiply those that 26 my miles cancel, and that leaves me with a gallon on top. 27 So now if I multiply across five 50 times five, 28 I get to 75 0. And that gives me units of gallons per hour, 29 which is what I wanted according to this part of our work. 30 And now the only equation that shows us the 2,750 is the, 31 so our correct answer is D.