You are watching: Is 36 a multiple of 9

## IM Commentary

This job examines the amazing fact that when a number is divisible by 9 climate the amount of its number is also divisible by 9. Only one and also two number numbers are examined here. A natural expansion of this task would be to see if this pattern continues to be true for 3 digit or larger numbers. In ~ this age, students room multiplying large numbers by a solitary digit number (4.NBT.5) and so they might be encouraged to pursue more this amazing fact about the sum of the number in number divisible through 9. Knowledge this rule provides terrific practice in place value and also properties that arithmetic.

Three services are noted for component (c), explaining the pattern. One offers a linguistic description, the second uses arithmetic manipulations, when the 3rd uses a picture. Students working on this task will watch for and make usage of framework (MP7): in components (b) and (c), students are looking both to determine a pattern and explain why the sample holds. Student will likewise look for and express regularity in repeated thinking (MP8), specifically in component (c); patterns in general require identify a process which is repetitive multiple times.

## Solutions

Solution:1 Arithmetic Properties

The an initial ten multiples the 9 are$$9, 18, 27, 36, 45, 54, 63, 72, 81, 90.$$

For the tens places, note that the number 9 have the right to be thought of as 0 tens and 9 ones for this reason the 10s place has actually a 0. The tens location of 18 is 1. Going through the list of multiples that 9, the tens digits are$$0, 1, 2, 3, 4, 5, 6, 7, 8, 9.$$For the persons place, we watch that 9 has 9 ones, 18 has 8 ones, and also going with the list we acquire ones worths of$$9, 8, 7, 6, 5, 4, 3, 2, 1, 0.$$So the tens ar starts in ~ 0 and go up by 1 when the ones ar starts in ~ 9 and also goes down by 1.

Another necessary pattern the relates the ones and also tens places is that if we add up the digit in the tens place and also the number in the ones place, we get 9 because that each of these numbers.

We will define why the digit in the tens ar goes increase by 1 and also the digit in the ones place goes down by 1.

To go to the next multiple of 9, we add 9 every time. We recognize that 9 = 10âˆ’1. So including 9 is like including 10 and then subtracting 1. Adding 10 increases the the digit in the tens ar by 1 (as long as that is not 9). Subtracting 1 to reduce the the number in the ones location by 1 (as lengthy as the is no 0).Solution:2 Equations and picture for component (c)

Here we usage the nature of arithmetic to aid explain why the tens value boosts by 1 and also the ones value decreases by 1 when adding 9. We study the equation 18+9=27 together an example. We can rewrite 18=1Ã—10+8 and 9 = 10 - 1 come get

eginalign18+9 &=(1Ã—10+8)+(1Ã—10âˆ’1) \&=1Ã—10+(8+1Ã—10)âˆ’1\&=1Ã—10+(1Ã—10+8)âˆ’1\&=(1Ã—10+1Ã—10)+(8âˆ’1)\&=(1+1)Ã—10+(8âˆ’1).endalign

We have actually written out every action to check out which rules of arithmetic space being used. The an initial line is arithmetic, the 2nd line provides the associative residential or commercial property of addition, the third line provides the commutative home of addition, the 4th line offers the associative property of addition, and the 5th line provides the distributive home of multiplication over addition. Notification that the very last line shows why the 10s place has increased by one if the ones places has lessened by one after adding 9.

The arithmetic steps over can be visualized in the table below:

Each many of 9 is emphasize in green. To relocate from one multiple of 9 come the next, in the table, we move down one (adding 10) and also to the left one (subtracting 1). The amount of the number is still the same since the digit in the tens place has actually increased through 1 when the digit in the ones ar has lessened by 1.

Solution:3 snapshot for (c)

Here we provide a visual depiction for the pattern in the multiples that 9. We an initial look in ~ what happens through 9+9:

To do a ten we have actually moved one green block indigenous the first 9 to the 2nd 9: this provides us a ten and eight ones. For this reason the 10s place has actually increased through one and the ones location has decreased by one. We can see the same pattern going from 18 to 27 by adding 9:

Here too we take away one native the 8 in 18 and include it to the 9 to make a 10. The final snapshot looks a small out that order through the 7 ones between the 2 tens but we can shift this around to put the two tens together. If we look at the collection of equations in the 2nd solution, the fact that the strips space switched around in stimulate to have the 10s together shows up once the commutative property of enhancement is used.

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This pattern will continue to be until us reach 90. As soon as we include 9 come 90 there space no persons to take from in stimulate to include to the 9 and make a 10.