Explanation for Question 26 From the Math (Calc) Section on the Official Sat Practice Test 6
Question 26 reads a gear ratio are to us is the ratio of the 2 number of teeth of two connected gears. The ratio of the number of revolutions 3 per minute, RPM of two gear wheels is S to R and 4 the diagram below gear a is turned by a motor, 5 the turning of gear, a causes gears B and C to turn as well. 6 And then it gives us this picture and you can kind of visualize what's 7 happening that as a turns, 8 its teeth move as well. And because its teeth are inner locked with the 9 teeth of gear B, that's what causes the skier B to turn. 10 And then as B is turning that's what caused the seat of turn? 11 So it's kind of a chain effect between the three different gears. 12 Then the question reads, if you're a is rotated at, 13 by the motor at a rate of 100 RPM, 14 what is the number of revolutions per minute for gear C? 15 So to solve this problem, we're trying to find out essentially how quickly 16 your C rotates, but because the motion moves from a to B and 17 then B to C, we first need to find the motion of B. 18 So let's set up the gear ratio for gears a and B. 19 And in this case, we'll say that gear a is R and gear B 20 is S so with that, 21 our, to us would be 20 to 60 because that's the ratio of the 22 teeth. 23 And then if you flip that for the ratio of the number of revolutions 24 per minute, we would get 60 to 20. 25 So in other words, when gear a is turning 60 26 revolutions per, or excuse me when, 27 um, yes. When, 28 when gear a is turning at 60 revolutions per minut...