Multiple choice

Ted is 30% as old as his father Toad. The percentage increase in the age of Toad, when he is thrice as old as Ted, is equal to which of the following?

  1. 5%

  2. 7.5%

  3. 10%

  4. 12.5%
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A Correct answer
Explanation

Let Ted = T, Toad = F. T = 0.3F. When Toad is 3T, let the time elapsed be x. (F+x) = 3(T+x). Substitute T=0.3F: F+x = 3(0.3F+x) = 0.9F + 3x. 0.1F = 2x, so x = 0.05F. The increase in Toad's age is x/F = 0.05, or 5%.

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