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2000 AMC 10 Problem 3

Problem 3 of 25EasierAlgebra

Each day, Jenny ate 20%20\% of the jellybeans that were in her jar at the beginning of that day. At the end of the second day, 3232 remained. How many jellybeans were in the jar originally?

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Solution

Since Jenny eats 20%20\% each day, 80%80\% remain at the end of each day. If xx is the original number, then (0.8)2x=0.64x=32,(0.8)^2 x = 0.64x = 32, so x=50.x = 50. Thus, the correct answer is B.

More practice

Concepts: percentage · work backwards

Problem text and solution from the LIVE past-contest archive. See also the AoPS wiki page for community solutions.