Multiple choice general knowledge math & puzzles

Farmer Charlie has a chicken farm. On a certain day, Charlie calculates in how many days he will run out of chicken-food. He notices that if he would sell 75 of his chickens, he could feed the remaining chickens twenty days longer with the chicken-food he has, and that if he would buy 100 extra chickens, he would run out of chicken-food fifteen days earlier. How many chickens does farmer Charlie have?

  1. 300

  2. 299

  3. 301

  4. 298
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let C be chickens and D be days. CD = (C-75)(D+20) and CD = (C+100)(D-15). Solving these equations: 20C - 75D = 1500 and -15C + 100D = 1500. Multiplying and solving leads to C = 300.

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