beginning with 9, list the an initial 10 multiples the 9. In the list in part (a) what patterns do you see through the number in the 10"s place? What patterns perform you see with the number in the 1"s place? utilizing pictures, words, or equations, define the trends you observed in part (b).

You are watching: Which number is divisible by 9

## IM Commentary

This task examines the exciting fact that once a number is divisible through 9 then the sum of its number is likewise divisible by 9. Only one and also two digit numbers are examined here. A natural extension of this activity would it is in to see if this pattern continues to be true for 3 digit or larger numbers. At this age, students room multiplying big numbers by a solitary digit number (4.NBT.5) and also so they could be encouraged to pursue more this exciting fact around the amount of the number in number divisible through 9. Knowledge this dominion provides terrific practice in place value and properties of arithmetic.

Three services are provided for part (c), explaining the pattern. One offers a verbal description, the second uses arithmetic manipulations, when the 3rd uses a picture. Students functioning on this job will look for and also make use of framework (MP7): in parts (b) and also (c), students space looking both to determine a pattern and explain why the pattern holds. College student will additionally look for and also express regularity in repeated reasoning (MP8), especially in part (c); trends in basic require identifying a procedure which is recurring multiple times.

## Solutions

Solution:1 Arithmetic Properties

The very first ten multiples that 9 are\$\$9, 18, 27, 36, 45, 54, 63, 72, 81, 90.\$\$

For the 10s places, keep in mind that the number 9 can be believed of together 0 tens and 9 ones so the 10s place has actually a 0. The tens ar of 18 is 1. Going v the list of multiples of 9, the 10s digits are\$\$0, 1, 2, 3, 4, 5, 6, 7, 8, 9.\$\$For the persons place, we see that 9 has actually 9 ones, 18 has actually 8 ones, and also going through the list we gain ones worths of\$\$9, 8, 7, 6, 5, 4, 3, 2, 1, 0.\$\$So the tens ar starts at 0 and also go up by 1 if the ones ar starts in ~ 9 and also goes down by 1.

Another crucial pattern that relates the ones and tens locations is that if we add up the digit in the tens place and the digit in the people place, we get 9 because that each of these numbers.

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

To walk to the next multiple that 9, we include 9 each time. We recognize that 9 = 10−1. So adding 9 is like adding 10 and also then individually 1. Including 10 boosts the the digit in the tens location by 1 (as long as that is no 9). Subtracting 1 reduce the the number in the ones ar by 1 (as lengthy as it is no 0).

Solution:2 Equations and photo for component (c)

Here we use the properties of arithmetic to help explain why the 10s value boosts by 1 and also the ones value decreases through 1 when adding 9. We research the equation 18+9=27 as an example. We can rewrite 18=1×10+8 and 9 = 10 - 1 to get

\beginalign18+9 &=(1×10+8)+(1×10−1) \\&=1×10+(8+1×10)−1\\&=1×10+(1×10+8)−1\\&=(1×10+1×10)+(8−1)\\&=(1+1)×10+(8−1).\endalign

We have written out every action to watch which rules of arithmetic space being used. The first line is arithmetic, the 2nd line supplies the associative building of addition, the third line offers the commutative residential property of addition, the 4th line provides the associative home of addition, and the fifth line offers the distributive home of multiplication over addition. Notice that the really last line shows why the 10s place has increased by one while the ones locations has lessened by one after including 9.

The arithmetic steps over can be visualized in the table below: Each many of 9 is emphasize in green. To relocate from one many of 9 to the next, in the table, we move down one (adding 10) and to the left one (subtracting 1). The amount of the digits is tho the same since the number in the tens place has increased by 1 when the digit in the ones location has lessened by 1.

Solution:3 picture for (c)

Here we offer a visual representation for the pattern in the multiples that 9. We very first look at what happens through 9+9: To make a ten we have moved one eco-friendly block indigenous the very first 9 come the second 9: this provides us a ten and eight ones. For this reason the 10s place has increased by one and the ones place has decreased by one. We deserve to see the same pattern going from 18 to 27 by including 9: Here too we take away one from the 8 in 18 and add it to the 9 to do a 10. The final snapshot looks a little out that order v the 7 ones in between the 2 tens yet we can transition this around to put the two 10s together. If us look in ~ the collection of equations in the 2nd solution, the fact that the strips are switched approximately in order to have actually the 10s together reflects up when the commutative residential property of enhancement is used.

See more: Does A 2008 Ford F150 Have A Cabin Air Filter Location, Cabin Filter Replacement: Ford F

This sample will stay until us reach 90. When we add 9 to 90 there are no ones to take from in stimulate to add to the 9 and also make a 10.