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McGraw-Hill Math Grade 7 Answer Key Lesson 2.2 Estimating Products
Exercise
Question 1.
34 × 71
Answer:
2,100
Explanation:
Round both numbers, 34 as 30 and 71 as 70.
Ignore the zeros and multiply the digits.
3 x 7 = 21
Count the zeros and tack them onto the end of your product.
34 x 71 = 2,100.
Question 2.
456 × 33
Answer:
15,000
Explanation:
Round both numbers, 456 as 500 and 33 as 30.
Ignore the zeros and multiply the digits.
5 x 3 = 15
Count the zeros and tack them onto the end of your product.
456 x 33 = 15,000.
Question 3.
47 × 67
Answer:
3,500
Explanation:
Round both numbers, 47 as 50 and 67 as 70.
Ignore the zeros and multiply the digits.
5 x 7 = 35
Count the zeros and tack them onto the end of your product.
47 x 67 = 3,500.
Question 4.
731 × 55
Answer:
42,000
Explanation:
Round both numbers, 731 as 700 and 55 as 60.
Ignore the zeros and multiply the digits.
7 x 6 = 42
Count the zeros and tack them onto the end of your product.
731 x 55 = 42,000.
Question 5.
78 × 357
Answer:
32,000
Explanation:
Round both numbers, 78 as 80 and 357 as 400.
Ignore the zeros and multiply the digits.
8 x 4 = 32
Count the zeros and tack them onto the end of your product.
78 x 357 = 32,000.
Question 6.
129 × 157
Answer:
20,000
Explanation:
Round both numbers, 129 as 100 and 157 as 200.
Ignore the zeros and multiply the digits.
1 x 2 = 2
Count the zeros and tack them onto the end of your product.
129 x 157 = 20,000.
Question 7.
323 × 489
Answer:
150,000
Explanation:
Round both numbers, 323 as 300 and 489 as 500.
Ignore the zeros and multiply the digits.
3 x 5 = 15
Count the zeros and tack them onto the end of your product.
323 x 489 = 150,000.
Question 8.
417 × 37
Answer:
16,000
Explanation:
Round both numbers, 417 as 400 and 37 as 40.
Ignore the zeros and multiply the digits.
4 x 4 = 16
Count the zeros and tack them onto the end of your product.
417 x 37 = 16,000.
Question 9.
53 × 49
Answer:
2,500
Explanation:
Round both numbers, 53 as 50 and 49 as 50.
Ignore the zeros and multiply the digits.
5 x 5 = 25
Count the zeros and tack them onto the end of your product.
53 x 49 = 2,500.
Question 10.
515 × 79
Answer:
40,000
Explanation:
Round both numbers, 515 as 500 and 79 as 80.
Ignore the zeros and multiply the digits.
5 x 8 = 40
Count the zeros and tack them onto the end of your product.
515 x 79 = 40,000.
Question 11.
745 × 821
Answer:
560,000
Explanation:
Round both numbers, 745 as 700 and 821 as 800.
Ignore the zeros and multiply the digits.
7 x 8 = 56
Count the zeros and tack them onto the end of your product.
745 x 821 = 560,000.
Question 12.
475 × 71
Answer:
35,000
Explanation:
Round both numbers, 475 as 500 and 71 as 70.
Ignore the zeros and multiply the digits.
5 x 7 = 35
Count the zeros and tack them onto the end of your product.
475 x 71 = 35,000.
Question 13.
2701 × 23
Answer:
60,000
Explanation:
Round both numbers, 2701 as 3000 and 23 as 20.
Ignore the zeros and multiply the digits.
3 x 2 = 6
Count the zeros and tack them onto the end of your product.
2701 x 23 = 60,000.
Question 14.
77 × 74
Answer:
5,600
Explanation:
Round both numbers, 77 as 80 and 74 as 70.
Ignore the zeros and multiply the digits.
8 x 7 = 56
Count the zeros and tack them onto the end of your product.
77 x 74 = 5,600.
Question 15.
521 × 555
Answer:
300,000
Explanation:
Round both numbers, 521 as 500 and 555 as 600.
Ignore the zeros and multiply the digits.
5 x 6 = 30
Count the zeros and tack them onto the end of your product.
521 x 555 = 300,000.
Question 16.
303 × 251
Answer:
90,000
Explanation:
Round both numbers, 303 as 300 and 251 as 300.
Ignore the zeros and multiply the digits.
3 x 3 = 9
Count the zeros and tack them onto the end of your product.
303 x 251 = 90,000.
Question 17.
727 × 462
Answer:
350,000
Explanation:
Round both numbers, 727 as 700 and 462 as 500.
Ignore the zeros and multiply the digits.
7 x 5 = 35
Count the zeros and tack them onto the end of your product.
727 x 462 = 350,000.
Question 18.
92 × 177
Answer:
18,000
Explanation:
Round both numbers, 92 as 90 and 177 as 200.
Ignore the zeros and multiply the digits.
9 x 2 = 18
Count the zeros and tack them onto the end of your product.
92 x 177 = 18,000.
Question 19.
42 × 420
Answer:
16,000
Explanation:
Round both numbers, 42 as 40 and 420 as 400.
Ignore the zeros and multiply the digits.
4 x 4 = 16
Count the zeros and tack them onto the end of your product.
42 x 420 = 16,000.
Question 20.
499 × 55
Answer:
30,000
Explanation:
Round both numbers, 499 as 500 and 55 as 60.
Ignore the zeros and multiply the digits.
5 x 6 = 30
Count the zeros and tack them onto the end of your product.
499 x 55 = 30,000.