GATE 2021 MN – Question 52
The hypothetical daily-infection quantity c follows $100\,dc/dt-7c=0$, with t in days. Find its doubling time in days, to the nearest integer.
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Correct answer: 9 to 11
Explanation
Separate the equation to obtain dc/c=0.07dt, so c(t)=c(0)e^(0.07t). For doubling, e^(0.07t)=2, giving t=ln 2/0.07=9.9021 days. The nearest integer is 10. This is the paper’s specified mathematical model, not an empirical disease forecast.