Answer:
D
Explanation:
For each triangle, you are given two sides and the included angle (the one between those 2 sides). That's side-angle-side, so it is S-A-S.
The SAS Rule for Similar Triangles says that for 2 triangles X and Y, if you have the SAS of one and the SAS of the other, then X and Y are similar (same shape and proportions) if
(a) the angle in X is congruent (same) as the angle in Y
(b) the ratio between the two given sides in X is the same as the ratio between the two given sides in Y
For this particular problem, the ratio PR/PQ = 18/21 = 6/7 if you simplify by dividing both top and bottom by 3.
So we are looking for another triangle where we have the same ratio. (Put the smaller number on top, in the fraction.)
Answer A: 12/15 simplifies to 4/5, wrong answer
Answer B: 9/12 simplifies to 3/4, wrong answer
Answer C: 6/10 simplifies to 3/5, wrong answer
Answer D: 15/17.5 looks harder, because there is a decimal in it. But we know 17.5 is just 17 and a half, so I would first multiply top and bottom by 2
We get 30/35. That looks a lot better. Now it is easier to see we can divide both top and bottom by 5.
We get 6/7! That is the correct answer, so D is the triangle similar to PQR.