a number has the digits 9 and 7. to the nearest 10 the number rounds to 100. what is the number
Rounding off a number to the nearest ten means to write down the multiple of ten that the given number is nearest to.
To teach rounding off to the nearest x, it is helpful to introduce rounding using a number line. This helps to build an understanding of the relative sizes of each number and and then to fully understand the process of rounding.
To round off to the nearest ten using a number line place the number on the number line and count how far abroad the closest multiple of 10 is higher up or below this number. The closest number in the ten times table is the answer.
For each number there is a choice of whether to round down or to round up.
Rounding down to the nearest x means to write down the number in the ten times tabular array that is beneath the given number. This volition be the number of tens that the given number contains.
Rounding up to the nearest ten ways to write down the number in the ten times table that is above the given number. This will be the ten that is i more the ten that the given number contains.
Beneath is the number 23. 23 contains '2' tens, which is 20.
The choice is whether to circular down to xx or to round up to the next x along, which is 30.
On the number line, characterization the 23, 20 and xxx.
When educational activity rounding off using a number line, you volition most likely be using a number line that is already completed with all whole numbers written on it. In this case we tin merely notice the number 23 and then look to the left and correct to discover the next numbers that accept a '0' digit in the units cavalcade.
Counting how far away 23 is from 20, we count: 22, 21 and xx.
23 is 3 whole numbers abroad from xx.
Counting how far away 23 is from thirty, nosotros count: 24, 25, 26 ,27, 28, 29 and 300.
23 is seven whole numbers away from 30.
23 is nearer to 20 than it is to 30 and so, 23 rounds off downwards to xx.
We can see that 25 is the midway indicate between xx and 30 and 23 is on the left of this point. We can see that considering it is less than 25, it will round down.
We will at present look at the example of 26. 26 contains a '2' in the tens column. 2 tens are 20.
The choice is whether to round down to 20 or whether to circular upwards to 30.
Counting downwardly to 20 nosotros have: 25, 24, 23, 22, 21 and twenty.
26 is half-dozen numbers larger than 20.
Counting up to thirty we accept: 27, 28, 29 and 30.
26 is 4 numbers below 30.
26 is nearer to 30 than it is to 20 then, 26 rounds up to 30.
Think that 25 is the midway signal between 20 and xxx. Nosotros tin can see that 26 is nearer to 30 than 20 considering it is on the right manus side of 25.
So we can see that on the number line, we can expect at the midpoint between two tens and look at the position of the given number in comparison to this midpoint.
The midpoint between any two tens will always by a number that ends in a 5 in the units digit.
When teaching rounding off using a number line, you tin can look at different tens and so marker the number that is directly in the middle to show this.
We demand to decide how to round off 25, which is directly in between 20 and 30.
Practice nosotros make up one's mind to round downwards to twenty or round up to 30? Nosotros accept to choose one of these multiples of x.
We make up one's mind to round 25 upwards.
The rule is that if a number ends in 5 or more then round it up and if a number ends in 4 or less, round it down.
The reason we round down numbers which end in 4 or less, is that they are on the left of the midpoint between ii tens.
Any number ending in 6 or more than is on the right of the midpoint and we round information technology up.
The reason we as well circular upward numbers with 5 in the units digit is because every bit soon as nosotros have any extra decimal digits fastened, the number will move to the right of the midway point.
For example, 25.1 is now nearer to 30 than information technology is to 20.
Past including 25 in the dominion to circular upward means that we as well correctly circular up all numbers such equally 25.1, 25.nine and 25.001.
Once we take learnt how to round off numbers using a number line, it is helpful to teach the link between the digits of a number, whilst still referring to the number line.
We will look at using the rounding off rule for the instance of 57.
The rounding off rule states that if the whole number ends in a 5 or more, then circular up, otherwise round downwardly.
57 ends in a '7' digit.
We have the choice of whether to circular down to fifty or up to 60.
Since seven is 5 or more it rounds up.
57 rounds off to threescore when written to the nearest ten.
57 is nearer to 60 than information technology is to 50.
When first teaching this rounding off rule, remember to refer to the number line to build the understanding of why the rule works.
We will look at the example of rounding off 83 below.
We look at the digit in the units column, which is a '3'.
The rounding off rule says that if this digit is four or less, then round downward.
Since the number ends with a iii in the units column, it rounds down.
83 rounds off to 80.
83 is nearer to 80 than it is to xc because information technology is left of the midway point of 85.
Here is an example of rounding 95 off to the nearest ten.
On a number line, 95 is directly in between 90 and 100.
90 and 100 are the showtime two numbers either side of 95 that are in the ten times table. 100 is 10 lots of 10.
Recall that the rounding off rule says that any number with a five or more in the units column will round up.
Even though 95 is directly in between 90 and 100, nosotros round it upwardly.
95 rounds off to 100 when written to the nearest 10.
Source: https://www.mathswithmum.com/rounding-off-nearest-10-number-line/
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