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: a merchant marks goods up by 80 % and then offers a discount on the marked price. the profit that the merchant makes after offering the discount is 35 %. what % discount did the merchant offer ?
Options: a. 20 %, b. 25 %, c. 30 %, d. 35 %, e. 40 %

A: b
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Q: Problem: two trains of equal length are running on parallel lines in the same directions at 46 km / hr. and 36 km / hr. the faster trains pass the slower train in 72 seconds. the length of each train is :
Options: a. 82 m, b. 50 m, c. 72 m, d. 100 m, e. none of these

A: d
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Q: Problem: a ranch has both horses and ponies. exactly 5 / 7 of the ponies have horseshoes, and exactly 2 / 3 of the ponies with horseshoes are from iceland. if there are 4 more horses than ponies, what is the minimum possible combined number of horses and ponies on the ranch ?
Options: a. 34, b. 38, c. 42, d. 46, e. 50

A:
d
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