2021 AMC 10A Spring Problem 13

Attempt Problem 13 of the 2021 AMC 10A Spring below, then check your answer against the video solution and professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2021 AMC 10A Spring solutions, or check the answer key.

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13.

What is the volume of tetrahedron ABCDABCD with edge lengths AB=2,AB = 2, AC=3,AC = 3, AD=4,AD = 4, BC=13,BC = \sqrt{13}, BD=25,BD = 2\sqrt{5}, and CD=5?CD = 5?

33

232\sqrt{3}

44

333\sqrt{3}

66

Answer: C
Concepts:volume3D geometryPythagorean Theorem
Difficulty rating: 1370
Video solution:
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Written solution:

Place A=(0,0,0),A=(0,0,0), B=(2,0,0),B=(2,0,0), C=(0,3,0),C=(0,3,0), and D=(0,0,4).D=(0,0,4). Then

BC=22+32=13,BD=22+42=25,CD=32+42=5, \begin{aligned} BC &= \sqrt{2^2+3^2}=\sqrt{13}, \\ BD &= \sqrt{2^2+4^2}=2\sqrt5, \\ CD &= \sqrt{3^2+4^2}=5, \end{aligned}

so this coordinate model matches all the given edge lengths. The tetrahedron is a rectangular-corner tetrahedron with perpendicular edge lengths 2,3,42,3,4 from A,A, so its volume is

16(2)(3)(4)=4.\frac16(2)(3)(4)=4.

Thus, C is the correct answer.

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