2013 AMC 8 Problem 15 — Solution & Video | LIVE by Po-Shen Loh

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2013 AMC 8 Problem 15

Below is the video solution and professionally curated solution for Problem 15 of the 2013 AMC 8, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2013 AMC 8 solutions, or check the answer key.

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Concepts:exponent

Difficulty rating: 1070

15.

If $3^p + 3^4 = 90$ , $2^r + 44 = 76$ , and $5^3 + 6^s = 1421$ , what is the product of $p$ , $r$ , and $s$ ?

$27$

$40$

$50$

$70$

$90$

Video solution:

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Written solution:

Subtract the known number from each equation: $3^p=90-81=9,\qquad 2^r=76-44=32,\qquad 6^s=1421-125=1296.$

Therefore $p=2$ , $r=5$ , and $s=4$ . Their product is $2\cdot5\cdot4=40$ .

Thus, B is the correct answer.

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