Question 1072885
The initial consumption is 20 tonnes, which increases by 2% per year. To sum up the series, we have:
250=20Σ(1.02)^n where n goes from 0 to ?. 250/20=12.5, so
12.5=Σ(1.02)^n
Plugging in different values for n, we find that n equals a little over 11 years before the oil reserve is used up.