Answering Without Measuring

Here's a question no ruler can help you with.

How many times do you breathe in a year?

You can't measure that. You can't count it either — you'd have to sit there for twelve months. And yet you can work it out this afternoon, on the back of an envelope, and land remarkably close to the truth.

That skill is called estimation, and it's one of the most useful things in all of science. Whenever a scientist meets a question too big to measure — how much rain falls on Bangladesh in a year, how many cells are in your body — this is what they reach for.

It's also, at your level, one of the highest-scoring skills in the whole olympiad. Estimation questions look impossible, so most students leave them blank. They aren't impossible. They just need a method, and by the end of this lesson you'll have it.

You'll be able to:

• explain what an estimate is, and why it isn't the same as a wild guess
• break a big question into small steps you can actually answer
• round numbers to make the arithmetic easy without wrecking the answer
• judge your own estimate by whether it lands within a factor of two