Estimation (Introduction)
Estimation is a Skill for Life.
As you walk around and live your life, imagine if you could easily estimate:
- how much a bill will be,
- which item is the best value for money
- the size, areas and angles of things
Also, it would be great if you could quickly guess how many people are in a room, how many cars in the street, how many boxes on the shelf, or even how many seagulls on the beach.
We aren't talking exact answers here, but answers that are good enough for your life.
Exact vs Estimate
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In mathematics we often stress getting an exact answer. But in everyday life a few cents won't make |
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Estimation is ...
... finding a number that's close enough right answer.
- You are not trying to get the exact right answer
- You just need a value that's good enough (usually in a hurry!)
Tip: How close is "close enough" depends on the situation.
- Shopping: being within a few dollars can be enough
- Measuring: for clothes a centimeter or two is ok, but when driving kilometers are fine
- Science: you may need a closer estimate, so use more careful rounding
Why?
Estimation can save you money. Always do a quick estimation of how much you should pay:
Example: you want to buy five magazines that cost $1.95 each. When you go to buy them the cost is $12.25. Is that right?
"five at $1.95 each is about 5 times 2, or about $10"
so $12.25 seems too much!
Ask to have the total checked.
Estimation can save you time (when the calculation doesn't have to be exact):
Example: you want to plant a row of flowers. The row is 58.3cm long. The plants should be 6cm apart. How many do you need?
"58.3 is nearly 60, and 60 divided by 6 is 10,
so 10 plants should be enough."
Estimation can save you from making mistakes with your calculator:
Example: you are calculating 107 times 56, and the calculator shows this:
952.00
Is that right?
"107 times 56 is a bit more than 100 times 50, which is 5000"
Ooops! you must have typed something wrong ...
... in fact you pressed 17×56 (you left out the zero in 107), and without estimating you could have made a really big mistake!
In fact don't trust calculators or computers ...
Computers don't understand what you are doing.
So use your brain power to double-check everything
And one last important reason:
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Estimation helps you focus on what's really going on. |
Fun, and Good for your Brain
It is actually good fun to do estimating because it keeps your mind active. As you walk around see how good you are at estimating answers before they come up.
- At the supermarket try to add up everything yourself, and then compare it to the final bill
- Estimate how long it will take you to get home
- When shopping, see which is the better bargain by estimating the price per quantity
- and so on!
Example: You are making invitation cards. It took you 3 minutes and 20 seconds to make one card, but you need to do 15 more ... how long will it take? Think:
"... it took a little more than 3 minutes for one card, and 3 × 15 is 45...
... add a bit more ... maybe 50 minutes and I will be done."
And then see how close your estimate was when you finish.
Skill and Practice
Look around you right now. Don't count, but quickly guess: how many books, pens, or chairs are in the room? Now count them. How close was your estimate?
Estimating takes skill ... but how do you get this skill?
Lots of Practice.
So we made some Estimation Games for you to practice with!
Practice is the best way to become good at estimating, because you need to develop your own "strategies", as different numbers need different methods:
Example:
- 550 + 298: 298 is nearly 300 so an estimate is 550+300 = 850
- 550 + 248: 50+48 is nearly 100 so an estimate is 500+200 +100 = 800
In one case it seemed easy to change one number and then add.
In the other case I added the hundreds together and then increased the result by 100
So the first step is to think "how do I go about making this estimate?"
Tips and Tricks
After doing some practice, read our page on Estimation Tips and Tricks
Estimating Counts, Lengths and More
Estimation isn't always about doing calculations.
It is important for you to be able to estimate how many things you can see, or how long something is or how big something is.
Example: How many objects are here:
You could count them, but what if you don't need an exact answer, just one that's close enough? Can you guess well?
Answer: 48
Read more on our page on Visual Estimation.