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

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

Estimation can save you money 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 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 it correct? "107 times 56 is a bit more than 100 times 50, which is 5,000" you must have typed something wrong ...

What is "Rounding" ? Rounding means making a number simpler but keeping its value close to what it was. The result is less accurate, but easier to use. Example: 7.3 rounds to 7 Because 7.3 is closer to 7 than to 8

But what about 7. 5. Is it closer to 7 or closer to 8 But what about 7.5? Is it closer to 7 or closer to 8? It is half-way in between, so what should we do?

How to Round Numbers Decide which is the last digit to keep Leave it the same if the next digit is less than 5 (this is called rounding down) But increase it by 1 if the next digit is 5 or more (this is called rounding up)

Rounding Decimals First work out which number will be left when we finish. Rounding to tenths means to leave one number after the decimal point. Rounding to hundredths means to leave two numbers after the decimal point. etc.

3.1416 rounded to hundredths is 3.14 as the next digit (1) is less than 5 3.1416 rounded to thousandths is 3.142 as the next digit (6) is more than 5 1.2735 rounded to tenths is 1.3 as the next digit (7) is 5 or more

To round to "so many decimal places" count that many digits from the decimal point: 1.2735 rounded to 3 decimal places is 1.274 as the next digit (5) is 5 or more

Rounding Whole Numbers 134.9 rounded to tens is 130 as the next digit (4) is less than 5 12,690 rounded to thousands is 13,000 as the next digit (6) is 5 or more 15.239 rounded to units is 15 as the next digit (2) is less than 5