Multiplying Tens Hundreds And Thousands
Multiplying by Whole Tens and Hundreds
This is a consummate lesson with instruction and exercises for fourth grade about multiplying by whole tens and hundreds. The lesson explains the shortcut, and also explains why it works. It contains enough of exercises for the students, including word problem.
| We have studied the SHORTCUTS for multiplying any number by 10, 100, or 1,000: | ||
| To multiply any number by ten, just tag ONE nil on the terminate. To multiply any number by 100, just tag TWO zeros on the stop. To multiply whatever number by 1,000, just tag THREE zeros on the end. | ||
| 10 × 481 = 4,810 | one00 × 47 = 4,700 | 1000 × 578 = 578,000 |
| Annotation specially what happens when the number you multiply already ends in a aught or zeros. The rule works the aforementioned; you still have to tag the nothing or zeros. | ||
| 10 × 800 = 8000 | 100 × 6,600 = 660,000 | one000 × forty = 40,000 |
1. Multiply.
| a. 10 × 315 = _______ iii,560 × 10 = _______ 35 × 100 = _______ | b. 100 × 6,200 = _______ 10 × ane,200 = _______ 100 × 130 = _______ | c. 1,000 × 250 = _______ 38 × 1,000 = _______ 10 × 5,000 = _______ |
| SHORTCUT for multiplying past twenty or 200 (You tin probably guess this one!) | |
| What is twenty × fourteen? Imagine the problem without the zip. | What is 200 × 31? Imagine the problem without the zeros. |
two. Now try information technology! Multiply by 20 and 200.
| a. 20 × 8 = _______ four × 20 =_______ 20 × 5 = _______ | b. 200 × 7 = ________ v × 200 = ________ eleven × 200 = ________ | c. 20 × 12 = _______ 35 × 20 = _______ 200 × 9 = _______ | d. 20 × 16 = _________ 42 × 200 = ________ 54 × 20 = _________ |
| Why does the shortcut work? It is based on the fact that you can multiply in any society. | |
| When multiplying by 20, we tin can modify the twenty into ten × ii. For instance: twenty × fourteen = 10 × ii × 14 In that problem, first multiply 2 × 14 = 28. Then the problem becomes 10 × 28, which we know is 280. 20 × 14 = 10 ×two × xiv = x × 28 = 280 That'southward it! | Permit's try the same with 200. For case, 200 × 31 = 100 × two × 31 In that problem, first multiply 2 × 31 = 62. The problem at present becomes 100 × 62, which is 6,200: 100 × two × 31 = 100 × 62 = 6,200 |
3. Try it yourself! Make full in.
| a. 20 × 7 = ______ × 2 × vii = 10 × ______ = ________ | b. xx × 5 = ______ × two × 5 = 10 × ______ = ________ | c. 200 × eight = ______ × 2 × 8 = 100 × ______ = ________ | d. 200 × 25 = ______ × 2 × 25 = 100 × ______ = ________ |
four. Mark's shed measures 20 ft past 15 ft. What is its surface area? Write a number sentence.
"A" ways area.
A = __________________________________
five. Write a number sentence, and detect
the area of Mark's driveway.
A = __________________________________
6. Mark was told he needed 4 truckloads of gravel to cover his driveway.
Ane truckload costs v × $20 plus $30 for the commitment. How much will
it cost him to cover the driveway with gravel?
| SHORTCUT for multiplying by whole tens and whole hundreds | |||
| The same principle works if you multiply past whole tens (30, forty, 50, 60, 70, 80, or 90): simply multiply 2, 3, 4, 5, six, 7, 8, or 9, and so tag a zero to the end result. Similarly, if you multiply by some whole hundred, FIRST multiply without those ii | |||
| 50 × 8 = forty0 | nine0 × 11 = 990 | 300 × 8 = 2,400 | 12 × 800 = 9,six00 |
7. Multiply.
| a. xl × 3 = ______ 8 × twenty = ______ | b. 70 × half dozen = _______ 50 × 11 = ______ | c. lxxx × 9 = _______ 30 × xv = _______ |
| d. 60 × xi = _______ 12 × twoscore = _______ | east. 200 × 9 = ______ seven × 400 = ______ | f. 700 × half-dozen = ______ 600 × 11 = ______ |
| k. 200 × 12 = ______ 15 × 300 = ______ | h. 3 × 1100 = ______ viii × 900 = ______ | i. 11 × 120 = ______ viii × 300 = ______ |
| It even works this way: | ||
| To multiply 40 × 70, simply multiply 4 × 7, and tag two zeros to the consequence: 40 × vii0 = 2,800 | To multiply 600 × forty, only multiply 6 × iv, and tag three zeros to the result: half-dozen00 × four0 = 24,000 | To multiply 700 × 800, simply multiply vii × 8, and tag four zeros to the outcome. 700 × 800 = 560,000 |
viii. Multiply.
| a. 20 × 90 = _________ lxx × 300 = ________ | b. threescore × 80 = ________ xxx × 900 = ________ | c. 400 × 50 = ________ 200 × 200 = ________ |
| d. 80 × 800 = ________ 200 × 500 = ________ | e. 100 × 100 = _______ 40 × thirty = ________ | f. 800 × 300 = ________ 90 × 1100 = ________ |
Write a number sentence for each question.
9. I hour has ______ minutes.
How many minutes are in 12 hours?
How many minutes are in 24 hours?
10. One hr has ______ minutes, and one infinitesimal has ______ seconds.
How many seconds are there in 1 hour?
xi. Ed earns $30 per hour.
a. How much volition he earn in a viii-hour workday?
b. How much will he earn in a 40-hour workweek?
c. How many days will he need to work in order to earn more $i,000?
12. Find the missing factor. Call back "backwards"! How many zeros do you lot demand?
| a. _______ × 3 = 360 _______ × 50 = 450 | b. 40 × _______ = 320 v × ________= 600 | c. ________ × 40 = 400 ________ × 2 = 180 |
| d. _______ × 30 = iv,800 _______ × 200 = 1,800 | e. 40 × ________ = two,000 6 × _________= 4,200 | f. ______ × 800 = 56,000 _______ × xx = 12,000 |
John wanted to prove that forty × lxx is indeed two,800 past
breaking the multiplication into smaller parts. He wrote 40 as
4 × 10 and 70 as 7 × ten, then multiplied in a different lodge:
40 × 70 = four × x × 7 × 10
= ten × 10 × (four × 7) = 100 × 28 = 2,800.
Y'all exercise the same, and prove that 600 × l is indeed thirty,000.
This lesson is taken from Maria Miller's book Math Mammoth Multiplication 2, and posted at www.HomeschoolMath.cyberspace with permission from the author. Copyright © Maria Miller.
Multiplying Tens Hundreds And Thousands,
Source: https://www.homeschoolmath.net/teaching/md/multiply_by_10.php
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