Explanation for Question 15 From the Math (Calc) Section on the Official Sat Practice Test 8
So question 15 tells us about a rectangular prison with certain dimensions. 2 And they're asking us for the mass of the block in grams, 3 the mass of the block into grams, and they give us the density. 4 And so one place that we might get tripped up is how do I 5 solve for mass? You might not know the equation for density. 6 And so if you don't know the equation for density, you can see that 7 density has grams in the numerator, right? 8 So our mass is going to be in our numerator and our 9 centimeters cubed. We know that's volume, right? 10 So it's M over V right, mass over volume. 11 And so if our density is equal to our mass over our volume, 12 and we know that our density is 2.8, 13 so 2.8 is equal to mass over volume. 14 The next thing that we need to do is find our volume. And once 15 we know our volume, we can simply solve for the mass. 16 And we find our volume by multiplying our three dimensions by each other. 17 So 30 by 40 by 50, 18 and that'll give us 60,000. So we can erase this volume and put in 19 60,000 in place of the volume. 20 So now I just have to multiply by 60,000 on both sides. 21 That way these will cancel and I'll just be left with M equals something. 22 And when I do that, we get 168,000. 23 So mass is you go to a 168,000 grams. 24 We know it's grams because that's what was in our density units. 25 And that is in fact what they're looking for. So our best answer's going 26 to be D.