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.
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