Question:hard

The regular mathematics faculty could not teach because of being sick. As a stop-gap arrangement, different visiting faculty taught different topics on 4 different days in a week. The scheduled time for class was 7:00 am, with a maximum permissible delay of 20 minutes. The monsoon made the city bus schedules erratic, so the classes started at different times on different days.

Mr. Singh did not teach on Thursday. Calculus was taught in the class that started at 7:20 am. Mr. Chatterjee took the class on Wednesday, but he did not teach probability. The class on Monday started at 7:00 am, but Mr. Singh did not teach it. Mr. Dutta did not teach ratio and proportion. Mr. Banerjee, who did not teach set theory, taught a class that started five minutes later than the class in which probability was taught. The teacher in Friday's class taught set theory. Wednesday's class did not start at 7:10 am. No two classes started at the same time.

79. Probability was taught by:

Show Hint

Eliminate Chatterjee, Singh and Banerjee from probability using the direct clues, then use the Monday 7:00 am start to fix Dutta's day.
Updated On: Jul 10, 2026
  • Mr. Dutta on Monday
  • Mr. Dutta on Thursday
  • Mr. Singh on Wednesday
  • Mr. Singh on Monday
Show Solution

The Correct Option is A

Solution and Explanation

Check the four listed teacher-day pairs against the fixed facts about set theory (Friday) and the five-minute gap rule, instead of deriving the whole grid first.

  1. Mr. Dutta on Monday: Chatterjee, Singh and Banerjee are all ruled out of probability (Chatterjee by direct statement, Singh because Friday's teacher has set theory, Banerjee because he cannot be five minutes after his own class), which leaves Dutta as the probability teacher; putting Dutta on Thursday instead of Monday would force a class five minutes earlier than his to start before 7:00 am, which is not allowed, so Monday is correct.
  2. Mr. Dutta on Thursday: this would push the probability class before the allowed 7:00 to 7:20 am window; Monday is the only day that works for Dutta.
  3. Mr. Singh on Wednesday: Wednesday belongs to Mr. Chatterjee, not Mr. Singh, by direct statement, so this pairing is impossible on the day alone.
  4. Mr. Singh on Monday: the clue states plainly that Mr. Singh did not teach the Monday class, so this is ruled out immediately, and separately Mr. Singh's real day, Friday, carries set theory, not probability.

Only the first option survives every check.

Let's summarize:

  • Three of the five teachers (Chatterjee, Singh, Banerjee) are excluded from probability by direct or derived clues, leaving Dutta.
  • The 7:00 am Monday start and the five-minutes-later rule for Banerjee's Thursday class only fit together if Dutta, not Banerjee, is on Monday.

So probability was taught by Mr. Dutta, on Monday.

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