To calculate the doubling time, we use the formula:
[tex]\[
\text{Doubling Time} = \frac{70}{\text{growth rate}}
\][/tex]
Given that the growth rate is 10% per year:
[tex]\[
\text{growth rate} = 10\%
\][/tex]
First, convert the percentage to a decimal for ease of calculation:
[tex]\[
10\% = 0.10
\][/tex]
However, since we are using the rule of 70, we can directly use the percentage value without converting it to a decimal.
Substitute the growth rate into the formula:
[tex]\[
\text{Doubling Time} = \frac{70}{10}
\][/tex]
Perform the division:
[tex]\[
\frac{70}{10} = 7
\][/tex]
So, the doubling time is:
[tex]\[
7 \text{ years}
\][/tex]
Therefore, among the given options:
1. 1000 years
2. 7 years
3. 70 years
The correct answer is:
[tex]\[
7 \text{ years}
\][/tex]
