Explanation for Question 18 From the Math (Calc) Section on the Official Sat Practice Test 6
Question 18 asks us some building codes require that for indoor stairways, 2 the tread depth must be at least nine inches. 3 And the riser height must be at least five inches, 4 according to the riser tread formula, which of the following inequalities represents the set 5 of all possible values for the riser height that meets this code requirement. 6 Okay. So the first and kind of easy requirement to look at is we 7 know that the riser height must be at least five inches. 8 So H has gotta be greater than, or equal to five. 9 From that alone, we can cross off answer choice a because a is saying 10 that the height could be between zero and five inches. 11 Whereas we know that the minimum is five. We can keep in BNC and 12 then we can eliminate D because we know the minimum is five and this 13 is listing the minimum is eight. 14 It's saying that eight has to be, um, 15 or that the riser height has to be greater than or equal to eight 16 when it actually has to be greater than or equal to five. Okay. 17 So for the second part of the problem, let's look at this expression that 18 we've derived down here. 19 We have the H is equal to one half 25 minus 20 D. Let's write that out in a slope intercept 21 form that we can more easily understand. So one half times 25 is going 22 to be equal to 12.5 minus one, 23 half D. So let's plug it in this tread 24 depth of nine inches and figure out what the height is at that point. 25 It's about 12.5 minus one half, 26 and then we have nine. 27 S...