Could you help me with question 9 on page 38 please? I don’t understand how to solve it even using back-solving

Yeah, this one is pretty tough! 🙂

To backsolve it successfully, it’s helpful to also plug in. Say that the base and height of triangle A are both 10. Then if you try, say, answer choice C, which says that p = 23, you know that r = 18, and therefore that the base of triangle B is 12.3 (23% more than 10) and the height is 8.2 (18% less than 10). Does that give you the same area for both triangles?

\text{Area}_A=\dfrac{1}{2}(10)(10)=50

\text{Area}_B=\dfrac{1}{2}(12.3)(8.2)=50.43

Not quite, but you’re close! For that reason, probably makes sense to try the next closest choice, D. Sure enough, that one works.

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