6 Form PACE WORK 25/05/20

Тема: Округлення до десятків

Today, we will be introducing the rules of rounding. Define rounding for the students. Discuss why rounding and estimation is so important.

What do you think these words have to do with math?

Rounding

Estimate

Nearest ten

Practice.

Present this question to the class: The gum Sheila wanted to buy costs $.26. Should she give the cashier $.20 or $.30?

After some discussion, introduce 22 + 34 + 19 + 81 to the class. How difficult is this to do in your head? If we changed it to be 20 + 30 + 20 + 80, is that easier?

Draw a simple hill on the blackboard. Write the numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 so that the one and 10 are at the bottom of the hill, on opposite sides, and the five ends up at the very top of the hill. This hill will be used to illustrate the two tens that the students are choosing between when they are rounding.

Tell students that today we will focus on two-digit numbers. They have two choices with a problem like Sheila’s. She could have given the cashier two dimes ($0.20) or three dimes ($0.30). What she is doing when she figures out the answer is called rounding - finding the closest “10” to the actual number.

With a number like 29, this is easy. We can easily see that 29 is very close to 30. But with numbers.

Pretend that they are on a bike. If they ride it up to the 4 (as in 24), and stop, where is the bike most likely to head? (Back down to where they started.) So when you have a number like 24, and you are asked to round it to the nearest 10, the nearest 10 is backwards, which gets you right back to 20.

Continue to do the hill problems with the following numbers. Model for the first three with student input, then continue with guided practice, or have students do the last three in pairs:

12

28

31

49

86

73

What should we do with a number like 35? Discuss this as a class, and refer back to Sheila’s problem at the beginning. The “rule” is that we round to the next highest 10, even though the five is exactly in the middle.

Have students do six problems like the ones in class. Offer an extension for students who are already doing well, to round the following numbers to the nearest 10:

151

189

234

185

347

Make up and write down your own problems on rounding and read them out for the rest of the class to solve.