I am currently preparing for a problem solving test and i have a question which seems to be difficult to answer at only 2 minutes given and without a calculator.<p>So, let's say we have data for a period of 3 years. The number of, for example, apples was 2,100,000 3 years ago and is 500,000 this year. I do have to calculate 'the closest estimate of the annual percentage drop between 3 years ago and this year'?<p>The choices are:
(1) 20%
(2) 25%
(3) 40%
(4) 55%<p>What would be the quickest way to solve it in 2 minutes without a calculator? I would be very thankful for any help and i don't have much time left until the actual test.<p>Thank you!