Reference / Curriculum / 3B / Chapter 15

3B · Chapter 15 · Lesson 3

Adding Money

Add money amounts, keeping dollars and cents aligned by unit.

MATH-3B-C15-L03Independent and tutor-supported

Today's mathematical question

A notebook costs $4.54 and a pencil case costs $2.58. What is the total cost?

Learning target

Add money amounts, keeping dollars and cents aligned by unit.

Before starting: Prior lesson: Making $10. Try the warm-up independently.

Prerequisite · 3 questions

Check earlier skills first

These are earlier ideas you need for today; revisit them if they are difficult.

  1. P1

    You have $2.76. How much more money do you need to make exactly $10.00?

    Reveal explanation

    Answer: $7.24

    10 dollars is 1,000 cents. Subtract 276 cents to get 724 cents, or $7.24.

  2. P2

    You have $5.49. How much more money do you need to make exactly $10.00?

    Reveal explanation

    Answer: $4.51

    10 dollars is 1,000 cents. Subtract 549 cents to get 451 cents, or $4.51.

  3. P3

    You have $5.74. How much more money do you need to make exactly $10.00?

    Reveal explanation

    Answer: $4.26

    10 dollars is 1,000 cents. Subtract 574 cents to get 426 cents, or $4.26.

Learn and understand

To add money, combine like place values: dollars with dollars and cents with cents. If the cents sum to 100 or more, exchange 100 cents for one extra dollar. Converting both amounts into cents first is an equally valid way to check. For $2.75 and $1.60, add dollars and cents: $4.35. When the cents total at least 100, exchange 100 cents for another dollar.

Represent it three ways

  1. Concrete: Build equal pieces, measures, counters or shapes with real objects when useful.
  2. Pictorial: Use a two-column dollars-and-cents chart. Add cents first, regroup if needed, and then add dollars.
  3. Abstract: Write the matching number sentence, calculation, comparison or mathematical description. Explain each number's unit.

Important vocabulary

total cost
sum of prices
regroup
trade 100 cents for $1
decimal point
separator between dollars and cents

Fully worked examples and checks

Try each new understanding check before revealing the explanation.

Worked example 1

Explore, calculate, verify

A notebook costs $4.54 and a pencil case costs $2.58. What is the total cost?

  1. Identify the whole, the units, and what the question asks.
  2. Add cents: 454 + 258 = 712 cents = $7.12.
  3. Check that the answer uses the right units and makes sense.

Answer: $7.12

Check your understanding 1

A notebook costs $8.33 and a pencil case costs $3.11. What is the total cost?

Reveal answer and explanation

$11.44 — Add cents: 833 + 311 = 1144 cents = $11.44.

Worked example 2

Explore, calculate, verify

A notebook costs $4.07 and a pencil case costs $3.38. What is the total cost?

  1. Identify the whole, the units, and what the question asks.
  2. Add cents: 407 + 338 = 745 cents = $7.45.
  3. Check that the answer uses the right units and makes sense.

Answer: $7.45

Check your understanding 2

A notebook costs $6.80 and a pencil case costs $2.57. What is the total cost?

Reveal answer and explanation

$9.37 — Add cents: 680 + 257 = 937 cents = $9.37.

Worked example 3

Explore, calculate, verify

A notebook costs $8.68 and a pencil case costs $1.12. What is the total cost?

  1. Identify the whole, the units, and what the question asks.
  2. Add cents: 868 + 112 = 980 cents = $9.80.
  3. Check that the answer uses the right units and makes sense.

Answer: $9.80

Check your understanding 3

A notebook costs $1.45 and a pencil case costs $0.88. What is the total cost?

Reveal answer and explanation

$2.33 — Add cents: 145 + 88 = 233 cents = $2.33.

Guided · 5 questions

Guided practice

Keep the model and earlier examples visible while practising.

  1. G1

    A notebook costs $1.59 and a pencil case costs $2.56. What is the total cost?

    Reveal explanation

    Answer: $4.15

    Add cents: 159 + 256 = 415 cents = $4.15.

  2. G2

    A notebook costs $4.68 and a pencil case costs $2.29. What is the total cost?

    Reveal explanation

    Answer: $6.97

    Add cents: 468 + 229 = 697 cents = $6.97.

  3. G3

    A notebook costs $6.60 and a pencil case costs $1.94. What is the total cost?

    Reveal explanation

    Answer: $8.54

    Add cents: 660 + 194 = 854 cents = $8.54.

  4. G4

    A notebook costs $6.96 and a pencil case costs $1.14. What is the total cost?

    Reveal explanation

    Answer: $8.10

    Add cents: 696 + 114 = 810 cents = $8.10.

  5. G5

    A notebook costs $2.71 and a pencil case costs $3.80. What is the total cost?

    Reveal explanation

    Answer: $6.51

    Add cents: 271 + 380 = 651 cents = $6.51.

Independent · 8 questions

Independent practice

Work these without hints and explain the method used. Write answers on paper.

  1. I1

    A notebook costs $3.92 and a pencil case costs $2.32. What is the total cost?

    Reveal explanation

    Answer: $6.24

    Add cents: 392 + 232 = 624 cents = $6.24.

  2. I2

    A notebook costs $6.66 and a pencil case costs $3.40. What is the total cost?

    Reveal explanation

    Answer: $10.06

    Add cents: 666 + 340 = 1006 cents = $10.06.

  3. I3

    A notebook costs $7.03 and a pencil case costs $3.46. What is the total cost?

    Reveal explanation

    Answer: $10.49

    Add cents: 703 + 346 = 1049 cents = $10.49.

  4. I4

    A notebook costs $6.22 and a pencil case costs $2.81. What is the total cost?

    Reveal explanation

    Answer: $9.03

    Add cents: 622 + 281 = 903 cents = $9.03.

  5. I5

    A notebook costs $8.59 and a pencil case costs $2.96. What is the total cost?

    Reveal explanation

    Answer: $11.55

    Add cents: 859 + 296 = 1155 cents = $11.55.

  6. I6

    A notebook costs $6.49 and a pencil case costs $3.53. What is the total cost?

    Reveal explanation

    Answer: $10.02

    Add cents: 649 + 353 = 1002 cents = $10.02.

  7. I7

    A notebook costs $6.24 and a pencil case costs $0.99. What is the total cost?

    Reveal explanation

    Answer: $7.23

    Add cents: 624 + 99 = 723 cents = $7.23.

  8. I8

    A notebook costs $3.50 and a pencil case costs $2.92. What is the total cost?

    Reveal explanation

    Answer: $6.42

    Add cents: 350 + 292 = 642 cents = $6.42.

Challenge · 2 questions

Challenge and error analysis

Go beyond arithmetic: justify a claim, correct reasoning, or connect two representations.

  1. C1

    Explain why $5.05 is 5 dollars and 5 cents rather than 5 dollars and 50 cents.

    Reveal explanation

    Answer: $5.05

    The first digit after the decimal is tens of cents, and the second is ones of cents.

  2. C2

    You have $10.00 and spend $5.75. Find the change by counting up, explaining each jump.

    Reveal explanation

    Answer: $4.25

    Count 25 cents to $6.00, then $4.00 more to $10.00, for $4.25 change.

Exit · 3 questions

Exit check

Solve independently, then return on another day to check retention.

  1. E1

    A notebook costs $4.45 and a pencil case costs $1.63. What is the total cost?

    Reveal explanation

    Answer: $6.08

    Add cents: 445 + 163 = 608 cents = $6.08.

  2. E2

    A notebook costs $6.22 and a pencil case costs $1.07. What is the total cost?

    Reveal explanation

    Answer: $7.29

    Add cents: 622 + 107 = 729 cents = $7.29.

  3. E3

    A notebook costs $6.03 and a pencil case costs $2.86. What is the total cost?

    Reveal explanation

    Answer: $8.89

    Add cents: 603 + 286 = 889 cents = $8.89.

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