Estimation

Classroom Activities

Lesson One

Objective: The students will count within 20 by making (building up from) 10 and read and write numerals 11 to 20 and their corresponding number words.

Materials: Magnetic cutout pictures to attach to the chalkboard, students practice books

Procedure: Display a set of picture cutouts, such as apples or flowers. Make sure the number of cutouts is less than ten. Have the student count the number of cutouts. Add picture cutouts one by one until the total is ten. Each time a picture is added, ask student to call out the total. Add another cutout right under the first cutout, showing one row of 10 and one more. Have students say "eleven". Write the number word "eleven" and the numeral "11" on the chalkboard. Have students copy both the number word and the number into their exercise books. Indicate to the students that eleven is written as "11" to show "a ten and one" as the row of ten items and an additional one item. The example would look like:

eleven

11

Add another cutout to the second row, neatly below the first row's second cutout. Have the students say "twelve" and write the number word and the numeral. Remind them that for twelve there is one row of ten and two additional items.

Continue to add picture cutouts one by one until the total is 20. Each time write the number, both as a number word and as a numeral. Have students say the number word aloud and also write both the number word and the numeral in their exercise books. When it is 20, explain that the symbol means "two tens and nothing" as seen by the two rows of ten items.

Display a set of picture cutouts with a total between 10 and 20. Have the students count to the total, one by one, while pronouncing the number word correctly. Repeat this with different numbers of cutouts.

Write the number that is between 10 and 20 on the board. Have the students draw the same number of dots in their exercise books. Have them draw a group of ten, and then the extra ones in a separate group. Repeat this with different numbers.

Display a set of picture cutouts distributed randomly on the board. Have one student come to the board to select 10 cutouts and rearrange them into a neat row. Have another student take cutouts, one by one, from the remaining cutouts. Ask the student to use the cutouts to form another row while counting the new total by starting from 10, one by one. When they are done, have them say the number name. Write the numeral and ask, what is the 1 telling us? What is the (number in the ones place) telling us? Ask whether they can hear the parts of the number in the name. That is, can they hear the "ten" in "fourteen"? (It sounds a little different doesn't it? But if you think about it, you can hear "ten". And can you hear the four more?

Repeat this process using different numbers of picture cutouts. At the end, highlight this method of separating out 10 objects first and then count onward from 10.

Lesson Two

Objective: The students will add two one digit numbers, using the "make a ten" strategy.

Materials: magnetic picture cutout cards for the chalkboard

Procedure: Display a set of 10 picture cutouts. Ask the students to count them. Add 2 picture cutouts under the first set. Ask student to count the number of added items. Referring to the two numbers, write the question on the board, 10 + 2 = ?. Ask the students to find out the answer by counting the total number of items. Then have them write the completed addition sentence in their exercise books.

10 + 2 = ?

10 + 2 = 12

Display two clusters of picture cutouts on the board. Ask the students to count the number of items in each cluster. (6, 7)

Referring to the two numbers write the question on the board, 6 + 7 = ?. Have the students find the total by counting the items. (13) Introduce another way of counting to get the total number of items. Ask students to count only the second cluster, starting with one more that the number of items in the first cluster. (7, 8, 9, 10, 11, 12, 13) Have the students write the completed addition sentence in their exercise book.

6 + 7 = ?

6 + 7 = 13

Repeat the process of counting starting with the next number, this time moving the items one by one to the other cluster as they are counted, until the total becomes 10.

Ask students to count the number of items left in the second cluster. (3) Then explain that the total can now be determined by adding 10 to the amount remaining in the second cluster. Have the students say: 6 + 7 = 13 is the same as 10 + 3.

Lesson Three

Objective: The students will count within 40 by making tens first. They will read and write number symbols 21 to 40 and the corresponding number words.

Materials: magnetic picture cutout cards for the chalkboard, number cards 20, 30, 40 and 1-9

Procedure: Display 16 picture cutouts. Have students count them. Add more cutouts, one by one, until the total is 20. This would become two rows of ten cutout pictures. Each time have the students call out the current total. Remind students that numbers 11 through 19 each has a special name. Write the numbers on the board in a column. Call a student to the board and have him or her write the number word next to each.

20

twenty

Add one more cutout. Tell students that the total now is twenty-one. Have students say twenty-one aloud. Show the students that this is 2 tens and 1 more. Now show the number cards for twenty-one by overlapping the number card for twenty with the number card for one. Write the numeral 21 on the board and write the corresponding number word.

21 twenty-one

Have the students copy the numeral 21 in their exercise books and write "twenty-one" next to it. Explain that we put a dash between "twenty" and "one" to show the connection between the two words. This is the way we write numbers that are above twenty.

Add one more cutout to the display. Tell the students that the total now is twenty-two. Have the students say twenty-two aloud. Write the numeral 22 on the board and show the corresponding number word card. Have the students copy the numeral 22 into their exercise books and write twenty-two next to it.

Continue this process of adding cutouts one by one until the total is 29, writing the numbers and number words to form a clear sequence to that the students can see the pattern. Now write the numbers 21 through 29 in a column. Have the students call out the number words and write them next to each corresponding number. Have students copy them in their exercise books in the same way.

This same procedure will be followed when introducing the numbers from 31 to 40.

Lesson Four

Objective: The students will add a one-digit number to a two-digit number without renaming.

Materials: number cards or chalk board

Procedure: Display 23 picture cards in a cluster. Have the students count them. Display five cutouts in another cluster. Have students count them also. Write the addition sentence on the board.

23 + 5 = ?

Rearrange the first set of cutouts into two rows of ten each and place the remaining three cutouts in a third row. Add the second set of cutouts to the third row. Have student count the items in the first two rows and verify for themselves that each row contains ten items. Then have them count the number of each cutout in the third row find that row's total.

Represent the situation using a number bond. Guide the students to say 23: is 2 tens and 3 ones. Then guide the students to say: 23 plus 5 is 2 tens and 3 ones plus 5 ones.

Write the addition sentence for the ones. Have the students provide the answer (8) without counting. Using the answer, modify the number bond.

3 + 5 = ?

Write the corresponding addition sentence and complete the number bond. Guide the students to say: 23 plus 5 is the same as 20 plus 8 ones.

20 + 8 = 28

Explain the addition process using this illustrated example

Repeat the process for other pairs of two-digit and one-digit numbers. Make sure that the total stays less than 40 and the sum of ones is less than 10.

Lesson Five

Objective: The students will count by tens, count within 100 by making tens, and read and write the number symbols and the number words. They will be able to tell how many tens and ones make up a given two-digit number.

Materials: 10 bundles of 10 straws each, base ten blocks, counters (beads, beans, buttons)

Procedure: Show the students the bundles of straws. Have 10 students count how many straws are in each bundle. Point out that the number of straws in each bundle is the same; that is they are equal groups. Therefore, by counting the bundles, we can find out how many individual straws there are. Ask the students if they can think about how this could be done. Then point out (even if they have) that we can count the straws in terms of tens because each bundle has ten straws. Write the list of numerals as follows:

1 ten = 10 ten

2 tens = 20 twenty

3 tens = 30 thirty

4 tens = 40 forty

5 tens = 50 fifty

6 tens = 60 sixty

7 tens = 70 seventy

8 tens = 80 eighty

9 tens = 90 ninety

10 tens = 100 one hundred

Show the students base ten rods (10 units) and again have them count how many in each rod. Show the students three rods and ask how many altogether. Encourage the students to count in tens. Repeat this exercise using a different number of rods (up to 10).