2013 AMC 8 Problem 6

Attempt Problem 6 of the 2013 AMC 8 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 2013 AMC 8 solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

6.

The number in each box below is the product of the numbers in the two boxes that touch it in the row above. For example, 30=6×5.30 = 6\times5.

What is the missing number in the top row?

22

33

44

55

66

Answer: C
Concepts:work backwards
Difficulty rating: 820
Video solution:
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Written solution:

The product of the numbers in the second row is 600,600, so the missing number in the middle right box is 600÷30=20.600 \div 30 = 20.

Now we know that the product of 55 and the missing number in the first row is 20.20. Therefore, the missing number is 20÷5=4.20 \div 5 = 4.

Thus, C is the correct answer.

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