[Video] Q5: If 5/x = 15/(x+20), what is the value of x/5?

Explanation for Question 5 From the Math (No Calc) Section on the Official Sat Practice Test 3

So number five tells us what X over five is. 2 And now it's asking us for the value of X over five, 3 right? So it gives us this, 4 um, equation. And it's asking us to find X over five. 5 And so the best way to go about this question is going to be 6 to solve for X on its own. And then from there solve for X 7 over five. So I will rewrite this equation that they've given us. 8 And I noticed that I have two fractions, is that equal to each other. 9 A good first step, whenever you have, that is always to cross-multiply. 10 So I'll do this denominator times. 11 The other numerators that's five times X plus 20 is equal to X times 12 15, which is 15 X. And now I want to think about using pen 13 dos to solve for X here, 14 I'll start with the P parentheses, which is distribution. 15 So five X plus 100 is equal to 15 X. 16 Now I'll move the five X to the other side. 17 That way my Xs are on one side of the equal sign and my 18 normal numbers are on the other side. I've got 100 is 19 equal to 10 X. Now the solve for X, 20 I just need to do my division divide by 10. 21 These tens will cancel 100 divided by 10 is 10. 22 So I've got 10 is equal to X, right? And so if you chose 23 answer choice, a maybe that's why you saw that 10 is what's what X 24 is equal to, but remember, we're looking for X over five and 10 divided 25 by five will give us two, which is why the best answer is going 26 to be C.