math question I can't answer

Question

 If there are 1.338 trillion barrels of oil in proven reserves and oil consumption

is 82.78 million barrels per day, what is the maximum number of years current

proven supply of oil runs out, if consumption does not decrease?

Answer 1

In one year, 82.78 x 10⁶ x 365 (ignoring leap years) = 3.02147 x 10⁸ (hundred million) barrels of oil are used.

The proven reserves are 1.338 x 10¹² (trillion) barrels of oil.

At the current rate of depletion, the reserves will last 1.338 x 10¹² / 3.021 x 10⁸ years.

This reduces to 0.4429 x 10⁴ ~ 4.429 x 10³ = 4,429 years.