Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

Q: Problem: if a and b are the roots of the equation x 2 - 9 x + 9 = 0, then the value of a 2 + b 2 is :
Options: a. 63, b. 24, c. 17, d. 6, e. 5

A: a
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Q: Problem: a merchant marks his goods up by 30 % and then offers a discount of 10 % on the marked price. what % profit does the merchant make after the discount ?
Options: a. 17 %, b. 25 %, c. 69 %, d. 31 %, e. 19 %

A: a
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Q: Problem: if x is invested in a bank at a rate of simple interest of y % p. a. for two years, then the interest earned is 800. if x is invested at y % p. a., for two years when the interest is compounded annually, the interest is 820. what is the value of x ?
Options: a. 8000, b. 6000, c. 5000, d. 4000, e. 3000

A:
a
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