Paper 1 · Mathematical Reasoning and Aptitude
UGC NET December 2021 June 2022 (12.10.2022) Shift-II
Every hour the number of bacteria in a sample doubles. If the original number is 100 and 50 bacteria are removed every two hours, how many bacteria are there after five hours?
A2500 bacteria
B2700 bacteria ✓ Correct
C1350 bacteria
D2800 bacteria
Correct answer: (B) 2700 bacteria — The answer is 2700 bacteria.
Explanation
★The answer is 2700 bacteria.
★Starting at 100, after two hours the count doubles twice to 400, then 50 are removed to give 350.
★After the third hour it doubles to 700.
★After the fourth hour it doubles to 1400, then 50 are removed to give 1350.
★After the fifth hour it doubles to 2700.
★So there are 2700 bacteria after five hours.
★So the answer is 2700 bacteria.
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