[Video] Q20: Michael swam 2,000 yards on each of eighteen days. the scatterplot above shows his swim time for and corresponding heart rate after each swim. the line of best fit for the data is also shown. for the swim that took 34 minutes, michael’s actual heart rate was about how many beats per minutes less than the rate predicted by the line of best fit?

Explanation for Question 20 From the Math (Calc) Section on the Official Sat Practice Test 3

Now for number 20, we're looking at a graph right in on our Y 2 axis. We've got the heart rate and on the X axis, 3 we have swimming time. So for you to read through the paragraph, 4 it tells us that Michael swam 2000 yards over the total of 18 days 5 and the scatter plot shows his heart rate after each swim. 6 And then it also tells us that we have a line of best fit, 7 which is this straight line. Right? And so that straight line kind of describes 8 the general trend of where the points are going. 9 Um, and then it tells us for the swim that took 34 minutes, 10 right? So we're looking at this swim right here, 11 which is going to be this data point. I'll make it slightly bigger. 12 Yep. Uh, so for that swim Michael's actual heart rate was how many less 13 than that predicted by the line of best fit. Right? 14 And so we see that our data point, his actual heart rate was right 15 about here, which appears to be at 1 48, 16 right? 2, 4, 6, 8, yes, 1 48. 17 But the line of best fit shows that at 34, 18 it should have been one 50. Now the difference between 1 48 and one 19 50 is two beats per minute. Right? 20 And so that's why our best answer that is going to be two, 21 because that's the difference between the actual point value and the value given to 22 us by the line.