Teacher Guide & Solutions

Mountain Addition Expedition Answer Key

Full vertical solutions with regrouping indicators for Climbs 1-5.

Document Type

Answer Key

Climb 1 75

Climb 2 75

Climb 3 83

Climb 4 92

Climb 5 95

Climb 1 Regrouping

1

48

+27

75

Solution Guide

Step-by-Step:

1. Ones: \(8 + 7 = 15\) ones

2. Regroup \(15\) as 1 ten, 5 ones.

3. Tens: \(1 + 4 + 2 = 7\)

Climb 2 Regrouping

1

59

+16

75

Solution Guide

Step-by-Step:

1. Ones: \(9 + 6 = 15\) ones

2. Regroup \(15\) as 1 ten, 5 ones.

3. Tens: \(1 + 5 + 1 = 7\)

Climb 3 Regrouping

1

35

+48

83

Solution Guide

Step-by-Step:

1. Ones: \(5 + 8 = 13\) ones

2. Regroup \(13\) as 1 ten, 3 ones.

3. Tens: \(1 + 3 + 4 = 8\)

Climb 4 Regrouping

1

67

+25

92

Solution Guide

Step-by-Step:

1. Ones: \(7 + 5 = 12\) ones

2. Regroup \(12\) as 1 ten, 2 ones.

3. Tens: \(1 + 6 + 2 = 9\)

Climb 5 Regrouping

1

26

+69

95

Solution Guide

Step-by-Step:

1. Ones: \(6 + 9 = 15\) ones

2. Regroup \(15\) as 1 ten, 5 ones.

3. Tens: \(1 + 2 + 6 = 9\)

Common Misconceptions

Forget to add regrouped ten: Students write 1 in dashboard but forget to add it, getting 65 instead of 75.
Two digits in ones column: Students write 15 below the line in ones column, ignoring regrouping.

Tip: "Ten ones jump over to the tens deck!"

Mountain Rescue Math Series — Instructor Key Page 1 of 2

Teacher Guide & Solutions

Mountain Subtraction Summit Answer Key

Full vertical solutions with borrowing indicators for Descents 6-10.

Document Type

Answer Key

Descent 6 34

Descent 7 36

Descent 8 36

Descent 9 35

Descent 10 47

Descent 6 Borrowing

6

12

72

-38

34

Solution Guide

Step-by-Step:

1. Ones: \(2 < 8\), must borrow!

2. Borrow \(1\) ten from \(7\) (leaves 6).

3. Ones become \(10 + 2 = \) 12.

4. Math: \(12-8=4\); \(6-3=3\).

Descent 7 Borrowing

5

11

61

-25

36

Solution Guide

Step-by-Step:

1. Ones: \(1 < 5\), must borrow!

2. Borrow \(1\) ten from \(6\) (leaves 5).

3. Ones become \(10 + 1 = \) 11.

4. Math: \(11-5=6\); \(5-2=3\).

Descent 8 Borrowing

7

13

83

-47

36

Solution Guide

Step-by-Step:

1. Ones: \(3 < 7\), must borrow!

2. Borrow \(1\) ten from \(8\) (leaves 7).

3. Ones become \(10 + 3 = \) 13.

4. Math: \(13-7=6\); \(7-4=3\).

Descent 9 Borrowing

4

14

54

-19

35

Solution Guide

Step-by-Step:

1. Ones: \(4 < 9\), must borrow!

2. Borrow \(1\) ten from \(5\) (leaves 4).

3. Ones become \(10 + 4 = \) 14.

4. Math: \(14-9=5\); \(4-1=3\).

Descent 10 Borrowing

8

10

90

-43

47

Solution Guide

Step-by-Step:

1. Ones: \(0 < 3\), must borrow!

2. Borrow \(1\) ten from \(9\) (leaves 8).

3. Ones become \(10 + 0 = \) 10.

4. Math: \(10-3=7\); \(8-4=4\).

Borrowing Errors

Smaller from Larger: Students calculate \(8-2=6\) instead of borrowing for \(72-38\), getting an incorrect ones digit of 6.
Zero Borrowing: For \(90 - 43\), students often write \(0-3=3\) without borrowing. Stress that zero means "nothing there to subtract from!"

Tip: "Cross off, rewrite, then subtract!"

Mountain Rescue Math Series — Instructor Key Page 2 of 2

Regrouping Rescue

Regrouping Rescue Worksheet

Regrouping Rescue Answer Key

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