Water lilies

Water lilies are growing on the pond and their number is doubled every day. The whole layer is covered in 12 days. How many days will it cover 8 layers?

Correct answer:

d =  3

Step-by-step explanation:

$$\begin{gathered} 2^d=8 \\ d=\ln (8)\mathrm{/}\ln (2)=3 \end{gathered}$$

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