Question

A cell's division time is $1$ minute. In $20$ minutes, a culture tube (culture medium) is $1/8^{th}$ filled with cells. When the tube will be fully filled?

• A. $21$ minutes
• B. $23$ minutes
• C. $60$ minutes
• D. $160$ minutes

Answer 1

Answer: (B)

$23$ minutes

Answer 2

In $20$ mins, culture tube is $1 /8^{th}$ filled with cells. Each cell divides every minute producing two daughter cells. Hence, in $21$ min $= \frac{1}{8} \times 2 = \frac{1}{4}$ In $22$ min $\frac{1}{4} \times = \frac{1}{2}$ In $23$ min $\frac {1}{2} \times 2 = 1$ That means, in $23$ minutes, the culture tube will be completely filled.