Estimation (Introduction)

Estimation is a Skill for Life.

shopping

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 are not talking exact answers here, but answers that are good enough for your life.

Exact vs Estimate

=
Equals
Symbol

In mathematics we often stress getting an exact answer.

But in everyday life a few cents here or there are not going to make much difference ... you should focus on the dollars!

Approximately
Equals Symbol

 

Estimation is ...

... finding a number that is close enough to the right answer.

  • You are not trying to get the exact right answer
  • What you want is something that is good enough (usually in a hurry!)

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.

money
money

Estimation can save you time (when the calculation does not 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 more than 100 times 50, which is 5,000"

 

Ooops! you must have typed something wrong ...

... in fact you pressed 17×56 (you left out the zero), and without estimating you could have made a really big mistake!

 

In fact don't trust calculators or computers ...  
Confusion

Computers don't understand what you are doing.

So use your brain power to double-check everything

Brain Power

And one last important reason:

Concentration

Estimation helps you focus on what is 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

Estimating takes skill ... but how do you get this skill?

Lots of Practice.

Estimation Game 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 is not 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:

How Many Objects

You could count them, but what if you don't need an exact answer, just one that is close enough? Can you guess well?

Answer: 48

Read more on our page on Visual Estimation