Why Estimate?

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

Exact vs. Estimate:

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 Estimate?

1. 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"

$12.25 seems too much!
Ask to have the total checked.

2. 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."

3. 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!

      
4. Estimation helps you focus on what is really going on. It is 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.

Wanna Practice?

http://www.sheppardsoftware.com/mathgames/round/mathman_round_addition.htm