All the solutions provided in McGraw Hill Math Grade 3 Answer Key PDF Chapter 3 Lesson 1 Subtract Mentally will give you a clear idea of the concepts.
McGraw-Hill My Math Grade 3 Answer Key Chapter 3 Lesson 1 Subtract Mentally
To subtract mentally, break up the smaller number into parts. Then subtract in parts.
Math in My World
Example 1
Et was a sunny, warm 86°F day for outdoor games. What was the temperature when it dropped 17°F ?
So, 86 – 17 = 69. The temperature was 69°F by the end of the day. You can also use subtraction rules to subtract mentally.
Example 2
Find 417 – 417.
Subtracting a number from itself equals 0.
So, 417 – 417 = 0.
You can mentally subtract a number that ends in 9 or 99.
Example 3
Find 140 – 129.
Make a ten.
129 is close to 130.
So, 140 – 129 = 11.
Example 4
Find 223 – 99.
Make a hundred.
99 is close to 100.
So, 223 – 99 = 124.
Guided Practice
Question 1.
Mentally subtract 34 – 18 by breaking apart the smaller number.
18 = 14 + ____
34 – 14 = ____
So, 34 – 18 = ____
Answer:
34 – 18 = 16.
Explanation:
Given the subtraction is 34-18, so by breaking apart the smaller number it will be
18 = 14 + X, which is
X = 18 – 14
= 4.
34 – 14 = 20,
So 34-18 will be 20-4 which is 16.
Talk Math
What mental subtraction strategy could you use to find 234 – 29?
Answer:
234 – 29 = 205.
Explanation:
Given that the equation is 234-29. Here, we will use the round and adjust strategy to subtract the equation. So
234 – 29 = 234 – 30
= 204, which is 204 + 1 = 205.
Question 2.
Mentally subtract 94 – 59 by making a ten.
94 – 60 = ____
____ + 1 = ____
So, 94 – 59 = ____
Answer:
94 – 59 = 34.
Explanation:
Given the equation is 94-59, so
94 – 59 = 94 – (59+1)
= 94 – 59 (+1)
= 35 – 1
= 34.
Independent Practice
Subtract mentally by breaking apart the smaller number.
Question 3.
792 – 94 = ____
Answer:
792 – 94 = 698.
Explanation:
Given the equation is 792 – 94, so
792 – 94 = 792 – (90+4)
= 792 – 90 (+4)
= 702 – 4
= 698.
Question 4.
885 – 52 = _____
Answer:
885 – 52 = 833.
Explanation:
Given the equation is 885 – 52, so
885 – 52 = 885 – (50+2)
= 885 – 50(+2)
= 835 – 2
= 833.
Question 5.
831 – 321 = ____
Answer:
831 – 321 = 510.
Explanation:
Given the equation is 831 – 321, so
831 – 321 = 831 – (300+21)
= 831 – 300 (+21)
= 531 – 21
= 510.
Question 6.
725 – 717 = ____
Answer:
725 – 717 = 8.
Explanation:
Given the equation is 725 – 717, so
725 – 717 = 725 – (710+7)
= 725 – 710(+7)
= 15 – 7
= 8.
Make a 10 or 100 to subtract mentally.
Question 7.
87 – 69 = ____
Answer:
87 – 69 = 18.
Explanation:
Given the equation is 87 – 69, to make 10 we will break 69 as 77-8. So
87 – 69 = 87 – (77-8)
= 87 – 77(-8)
= 10 + 8
= 18.
Question 8.
745 – 239 = ____
Answer:
745 – 239 = 506.
Explanation:
Given the equation is 745 – 239, to make 100 we will break 239 as 645-406. So
745 – 239 = 745 – (645-406)
= 745 – 645(-406)
= 100 + 406
= 506.
Question 9.
652 – 599 = __________
Answer:
652 – 599 = 53.
Explanation:
Given the equation is 652 – 599, to make 100 we will break 599 as 552+47. So
652 – 599 = 652 – (552+47)
= 652 – 552(47)
= 100 – 47
= 53.
Question 10.
384 – 199 = _______
Answer:
384 – 199 = 185.
Explanation:
Given the equation is 384 – 199, to make 100 we will break 199 as 284-85. So
384 – 199 = 384 – (284-85)
= 384 – 284(-85)
= 100 + 85
= 185.
Write the number sentences under their subtraction rule.
Question 11.
Answer:
The number sentence is 1,937 – 1,937 = 0 and 491 – 491 = 0.
Explanation:
The number sentence that we get when we subtract a number from itself is
1,937 – 1,937 = 0 and 491 – 491 = 0.
Question 12.
Answer:
The number sentence is 9,999 – 0 = 9,999 and 4,274 – 0 =4,274.
Explanation:
By subtracting 0 from a number we will get the number sentence as
9,999 – 0 = 9,999 and 4,274 – 0 =4,274.
Problem Solving
Use a mental subtraction strategy to solve.
Question 13.
How much could Maurice have saved on his shoes if he waited until today to buy them?
Answer:
If he waited for today, he can buy them for $24.
Explanation:
In the above image, we can see that the price tag is $73 and on sale day the price tag is $49. So if he waited for today, he can buy them for 73-49 which is
73-49 = 73 – (50-1)
= 73 – 50(-1)
= 23 + 1
= 24.
So if he waited for today, he can bought them for $24.
Question 14.
Mathematical PRACTICE 1 Keep Trying Blair started the morning with $75. Every activity she did today cost
money. Find how much money she had at the end of the day.
Answer:
By the end of the day, Blair had $22.
Explanation:
Given that Blair started the morning with $75 and every activity she did today cost money. As her activities cost is $9+$14+$17+$13 which is $53. So by the end of the day, Blair had $75-$53 which is
$75-$53 = 75 – (50+3)
= 75 – 50(+3)
= 25 – 3
= 22.
So by the end of the day Blair had $22.
HOT Problems
Question 15.
Mathematical PRACTICE 5 Use Mental Math Write each difference as you subtract mentally.
Answer:
Here, we have subtracted the difference that has got from the before equation.
479 – 9 = 470,
470 – 20 = 450,
450 – 37 = 413,
413 – 199 = 214,
214 – 21 = 193,
193 – 30 = 163,
163 – 99 = 64,
64 – 36 =28,
28 – 12 = 16,
16 – 9 = 7,
7 – 7 = 0.
Question 16.
? Building on the Essential Question How can I subtract mentally?
Answer:
We can subtract mentally by breaking the numbers apart by that we can perform subtraction easily.
McGraw Hill My Math Grade 3 Chapter 3 Lesson 1 My Homework Answer Key
Practice
Subtract mentally by breaking apart the smaller number.
Question 1.
82 – 47 = ____
Answer:
82 – 47 = 35.
Explanation:
Given the equation is 82 – 47, so
82 – 47 = 82 – (40+7)
= 82 – 40 (+7)
= 42 – 7
= 35.
Question 2.
165 – 26 = ___
Answer:
165 – 26 = 139.
Explanation:
Given the equation is 165 – 26, so
165 – 26 = 165 – (20+6)
= 165 – 20(+6)
= 145 – 6
= 139.
Question 3.
387 – 308 = ___
Answer:
387 – 308 = 79.
Explanation:
Given the equation is 387 – 308, so
387 – 308 = 387 – (300+8)
= 387 – 300(+8)
= 87 – 8
= 79.
Question 4.
674 – 426 = ____
Answer:
674 – 426 = 248.
Explanation:
Given the equation is 674 – 426, so
674 – 426 = 674 – (400+26)
= 674 – 400 (+26)
= 274 – 26
= 248.
Make a 10 or 100 to subtract mentally.
Question 5.
76 – 59 = ____
Answer:
76 – 59 = 17.
Explanation:
Given the equation is 76 – 59, to make 10 we will break 59 as 66-7. So
76 – 59 = 76 – (66-7)
= 76 – 66(-7)
= 10 + 7
= 17.
Question 6.
120 – 39 = ___
Answer:
120 – 39 = 81.
Explanation:
Given the equation is 120 – 39, to make 100 we will break 39 as 20+19. So
120 – 39 = 120 – (20+19)
= 120 – 20(19)
= 100 – 19
= 81.
Question 7.
554 – 199 = _____
Answer:
554 – 199 = 355.
Explanation:
Given the equation is 554 – 199, to make 100 we will break 199 as 454-255. So
384 – 199 = 554 – (454-255)
= 554 – 454(-255)
= 100 + 255
= 355.
Question 8.
453 – 19 = ____
Answer:
453 – 19 = 343.
Explanation:
Given the equation is 453 – 19, to make 100 we will break 19 as 353-334. So
453 – 19 = 453 – (353-334)
= 453 – 353(-334)
= 100 + 334
= 434.
Problem Solving
Use any mental math strategy to solve.
Question 9.
Mathematical PRACTICE 5 Use Mental Math The red team has 522 fans in the bleachers. The blue team has 425 fans in the bleachers. How many fewer fans does the blue team have?
Answer:
The fewer fans the blue team had is 97 fans.
Explanation:
Given that the red team has 522 fans in the bleachers and the blue team has 425 fans in the bleachers. So the fewer fans the blue team had is 522-425 which is 97 fans.
Question 10.
Mathematical PRACTICE 2 Use Number Sense There are 172 houses in Kyle’s neighborhood. He delivers papers to 99 houses. To how many houses does Kyle not deliver papers?
Answer:
The number of houses does Kyle not deliver papers is 73 papers.
Explanation:
Given that there are 172 houses in Kyle’s neighborhood and he delivers papers to 99 houses. So the number of houses does Kyle not deliver papers is 172-99 which is 73 papers.
Vocabulary Check
Draw a line to match the word to its definition or meaning.
Answer:
Test Practice
Question 13.
Avery has a digital camera with a memory card that can hold 284 pictures. If Avery has taken 159 pictures, how many pictures can the memory card still hold?
A. 124 pictures
B. 125 pictures
C. 135 pictures
D. 443 pictures
Answer:
B.
Explanation:
Given that Avery has a digital camera with a memory card that can hold 284 pictures and if Avery has taken 159 pictures. So the number of pictures can the memory card still hold is 284-159 which is 125 pictures.