Explanation for Question 19 From the Math (No Calc) Section on the Official Sat Practice Test 6
Question 19 asks us how many leaders have a twenty-five percent saline solution 2 must be added to three liters of a 10% saline solution to obtain a 3 15% saline solution. 4 Okay. So let's kind of visualize what's going on here. 5 We have some sort of solution that has 25% 6 saline, so it's more highly concentrated. 7 And we're adding that into another solution that 8 this one we know is three liters. So this one, 9 we don't know how many lyrics there are this one moment, 10 there are three liters and there's a 10% saline solution. 11 So you can see that there's less particles in this one, 12 or it's less densely concentrated particles. 13 Then in this first 25% salient solution, 14 this one being 10%. And we want to figure out what combination 15 of these two results in a 15% saline solution. 16 So somewhere in between those two in terms of concentration, 17 so it should be 15%. All right, 18 now we know that the final volume is going to depend 19 on this initial volume. That's going to be added in because it's going to 20 be the total volume will be X liters, 21 plus three liters. 22 Now we also know that we're trying to find, 23 or were given, I should say a concentration that 15% saline 24 solution. So the amount of sailing is going to be equivalent 25 to the volume times the concentration. 26 So let's define our unknown volume as X as I've done here. 27 We know that X times 0.25. 28 So that's that unknown volume times the 25% ceiling solution plus 29 three, that's the kn...