Estimating and Rounding

In maths we have been doing estimating and rounding. We started by rounding numbers to the nearest 10,100 or 1000 depending on what level we are in. For example:

347 rounded to the nearest 100

would be 300 because looking at the digit next to the hundred (The tens) it would round down. 1,2,3, and 4 round down and 5,6,7,8 and 9 round up.

347 rounded to the nearest ten

would be 350 because looking at the digit next to the tens (The units) it would round up.

Once we got the hang of that we rounded decimals and significant figures. When rounding decimals it’s the exact same as above apart from you look at numbers after the decimal point. For example:

2.8364 rounded to a whole number

would be 3 because looking at the tenths it rounds up.

2.8364 rounded to 1 decimal place

would be 2.8 because looking at the hundredths it rounds down.

For significant figures you have to count along:

26.4578

12 3456

For 1 significant figure we are looking to round so that there’s only one number and the rest are 0s. This sum equals 30.0000. It works the same for all significant figures (1 sig fig, 2 sig fig, 3 sig fig). We always start counting from the first digit that isn’t 0.

We have been also doing estimating so if we got given a large or complicated sum we would be able to estimate so when we actually do the sum we can check our answer. For example:

254.23 + 34.78 =

That’s quite hard so if we round to 2 sig fig the sum becomes:

250 + 35  285

To help us we have played lots of games some we played online others we played against each other. One of the games we played was a game called ZAP!!! Our teacher Mr. Flett made it up and it’s so easy that you can play at home. Here’s the rules:

 

1. Get some lolly sticks and on them write numbers like 12.34 or 56.8. On about 2 or 3 sticks write the word zap. Only write one number on each stick.
2. Put them all in a cup with the end you wrote the numbers on facing down.
3. On a piece of paper write the numbers 1 to 6 like you would in instructions.
4. Beside each number write something like “Round to sig fig” or “Round to 2 decimal places” Also write beside one free point and miss a go. Make sure it’s different for each number.
5. Write everyone’s name or initial that is playing the game on another piece of paper to keep points.
6. Now you can start. The first player picks a stick out the cup. You then need to roll a dice. The number that it shows will correspond with an instruction on the paper. Do what it says. If it was rounding then the people you are playing with need to check. If you get it right you win a point. If the stick you pick out says Zap then you lose all your points!

I hope you enjoyed this game! If you find this game easy then you could pick 2 sticks out, roll the dice, follow the instruction and then add or subtract the two numbers.

 

 

Some links to online rounding and estimating games:

 

• https://www.sheppardsoftware.com/mathgames/menus/roundestimate.htm
• http://www.transum.org/software/SW/Starter_of_the_day/Students/Rounding
• http://www.topmarks.co.uk/Flash.aspx?f=DartboardRoundingv2

By Rhianna