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Mathematics notes, unit 4

Money

Textbook Mathematics Year 3 (DLP), Part 1 and Part 2, pages Part 2, 1–24

What this chapter covers

  • You can add money up to RM10 000, with ringgit and sen (4.1)
  • You can subtract money and find the balance or the difference in price (4.2)
  • You can add and subtract money in one number sentence (4.3)
  • You can multiply money by a 1-digit number, 10, 100 and 1 000 (4.4)
  • You can divide money by a 1-digit number, 10, 100 and 1 000 (4.5)
  • You can name the currencies of ASEAN and other countries and read the value of RM1 in them (4.6)
  • You can tell needs from wants and explain why we save, invest and donate (4.7)
  • You can create stories from number sentences and solve money problems (4.8)

We use money every day: at the school canteen, at the pasar malam and when we get duit raya. In this unit you will add, subtract, multiply and divide money, learn about money from other countries, and learn to spend and save wisely.

Ringgit (RM) and sen are Malaysian money. RM1 = 100 sen. We write RM4 351.40 to mean 4 351 ringgit and 40 sen. The dot is called the decimal point. It separates ringgit from sen.
Malaysian notes RM1, RM5, RM10, RM20, RM50, RM100 and coins 5 sen, 10 sen, 20 sen, 50 sen
Malaysian notes and coins

4.1Adding money

Adding money is just like adding whole numbers. Total means "add everything together".

Example 1: a new bicycle (textbook p. 2)

A bicycle costs RM361, a helmet RM125 and a jersey RM79. What is the total cost?

  1. Write the amounts in columns. Ones under ones, tens under tens.
  2. Add from the right. Carry when a column makes 10 or more.
RM361 plus RM125 plus RM79 equals RM565 in columns

RM361 + RM125 + RM79 = RM565.

Example 2: ringgit and sen (textbook p. 3)

RM2 073.05 + RM948.60 + RM1 329.75 = ?

  1. Line up the decimal points.
  2. Add the sen first: 5 sen + 60 sen + 75 sen = 140 sen = RM1.40. Write 40 and carry 1 to the ringgit.
  3. Add the ringgit.
RM2 073.05 plus RM948.60 plus RM1 329.75 equals RM4 351.40

The answer is RM4 351.40.

Do not forget the decimal point! Always keep the decimal points in one straight line, and put the RM sign in your answer.

Missing number: RM3 480 + ? = RM7 500. To find the missing number, subtract: RM7 500 − RM3 480 = RM4 020.

a) RM1 043 + RM926 = ?   b) RM7 216.30 + ? = RM9 457.80
Show answerHide answer
a) RM1 043 + RM926 = RM1 969
b) RM9 457.80 − RM7 216.30 = RM2 241.50

4.2Subtracting money

Balance is the money you get back, or the money left over. Difference is how much more (or less) one price is than another. We find both by subtracting.

Example 3: piano and guitar (textbook p. 4)

A piano costs RM3 800 and a guitar costs RM760. What is the difference in price?

  1. Split RM3 800 into RM3 000 and RM800.
  2. RM800 − RM760 = RM40.
  3. RM40 + RM3 000 = RM3 040.

The difference in price is RM3 040.

Example 4: electricity bills (textbook p. 5)

RM296.45 − RM187.60 = ?

40 sen is less than 60 sen, so we regroup: take RM1 from the ringgit and change it into 100 sen.

RM296.45 minus RM187.60 equals RM108.85

The answer is RM108.85.

Example 5: Encik Zaki buys books (textbook p. 5)

Encik Zaki pays RM700 for books that cost RM638.80 and a bookmark that costs 95 sen. What is his balance?

  1. RM700.00 − RM638.80 = RM61.20
  2. RM61.20 − RM0.95 = RM60.25

His balance is RM60.25.

Did you know? You can check a subtraction with addition. RM2 596.50 − RM2 158.90 = RM437.60, because RM2 158.90 + RM437.60 = RM2 596.50.
95 sen is RM0.95, not RM95! Write sen as ringgit with "0." in front before you subtract.
a) RM1 947 − RM627 = ?   b) Two antique clocks cost RM9 258 and RM6 560.20. What is the difference in price?
Show answerHide answer
a) RM1 947 − RM627 = RM1 320
b) RM9 258.00 − RM6 560.20 = RM2 697.80

4.3Adding and subtracting together

Some problems need both addition and subtraction. Work from left to right.

Cash in is money put into a bank account (add it). Cash out is money taken out (subtract it).

Example 6: Asif's account book (textbook p. 7)

Account book: 31/5/2019 balance RM1 020.00; 2/6/2019 cash in RM280.00, balance RM1 300.00; 17/8/2019 cash out RM400.00, balance RM900.00
  1. RM1 020 + RM280 = RM1 300 (cash in, so add)
  2. RM1 300 − RM400 = RM900 (cash out, so subtract)

Asif's balance on 17 August 2019 is RM900.

Example 7: three tablets (textbook p. 7)

Model A costs RM3 460.80. Model B is RM680.90 cheaper than A. Model C is RM1 027.60 more expensive than B. Find the price of C.

  1. Cheaper means subtract: RM3 460.80 − RM680.90 = RM2 779.90 (model B)
  2. More expensive means add: RM2 779.90 + RM1 027.60 = RM3 807.50

Model C costs RM3 807.50.

Check by estimating. Round to the nearest hundred. RM7 945.30 + ? − RM324 = RM8 895 becomes RM7 900 + ? − RM300 = RM8 900, so ? is about RM1 300. The exact answer, RM1 273.70, is close, so it is reasonable.
RM909 + RM751 − 75 sen = ?
Show answerHide answer
RM909 + RM751 = RM1 660
RM1 660.00 − RM0.75 = RM1 659.25

4.4Multiplying money

Multiplying is quick repeated adding. 2 hampers at RM211 each cost 2 × RM211 = RM422.

Example 8: 3 items at RM82.30 each (textbook p. 10)

  1. Multiply the sen: 3 × 30 sen = 90 sen.
  2. Multiply the ringgit: 3 × RM82 = RM246.
  3. Put them together: RM246.90.
RM82.30 times 3 equals RM246.90

Example 9: when the sen make ringgit (textbook p. 10)

9 × RM317.80 = ?

9 × 80 sen = 720 sen = RM7.20. Write 20 sen and carry RM7 to the ringgit. The answer is RM2 860.20.

Multiplying by 10, 100 and 1 000

TimesExampleWhat happens
× 1010 × RM148.25 = RM1 482.50Digits move 1 place to the left
× 100100 × RM76 = RM7 600Digits move 2 places to the left (for whole ringgit, add two zeros)
× 1 0001 000 × RM9 = RM9 000Digits move 3 places to the left (for whole ringgit, add three zeros)
a) 6 × RM807.15 = ?   b) 100 × RM68 = ?
Show answerHide answer
a) 6 × 15 sen = 90 sen; 6 × RM807 = RM4 842; answer RM4 842.90
b) 100 × RM68 = RM6 800

4.5Dividing money

Dividing means sharing equally. Each share gets the same amount.

Example 10: kenduri costs

Six families share the cost of a kenduri equally. The total cost is RM1 350. How much does each family pay?

Bar model: RM1 350 split into 6 equal parts

RM1 350 ÷ 6 = RM225. Check: 6 × RM225 = RM1 350.

Example 11: price of one mango (textbook p. 12)

5 mangoes cost RM8. What is the price of one mango?

Method 1: change to sen. RM8 = 800 sen. 800 sen ÷ 5 = 160 sen = RM1.60.

Method 2: write RM8.00 and divide, keeping the decimal point in line. RM8.00 ÷ 5 = RM1.60.

Example 12: remote control cars (textbook p. 12)

8 remote control cars cost RM1 008.40. RM1 008.40 ÷ 8 = RM126.05. Check: 8 × RM126.05 = RM1 008.40.

Dividing by 10, 100 and 1 000: move the decimal point 1, 2 or 3 places to the left.
RM730 ÷ 10 = RM73  ·  RM10 000 ÷ 100 = RM100  ·  RM3 650 ÷ 1 000 = RM3.65
In RM1 008.40 ÷ 8, there is a 0 in the sen place of the answer: RM126.05. If you forget it you get RM126.5, which is wrong.
a) RM471.60 ÷ 8 = ?   b) RM3 105 ÷ 100 = ?
Show answerHide answer
a) RM471.60 ÷ 8 = RM58.95
b) RM3 105 ÷ 100 = RM31.05

4.6Money of other countries

Currency is the kind of money a country uses. Malaysia's currency is the ringgit.
ASEAN countryCurrencyOther countryCurrency
MalaysiaringgitUnited States of Americadollar
Singapore, BruneidollarAustraliadollar
ThailandbahtGreat Britainpound
IndonesiarupiahJapanyen
PhilippinespesoSaudi Arabiariyal
Vietnamdong
Laoskip
Cambodiariel
Myanmarkyat

The value of RM1

When we travel, we exchange (swap) our ringgit for another currency. The table shows how much RM1 was worth in July 2018.

Value of RM1: Singapore 0.34 dollar, Thailand 8.22 baht, Indonesia 3 551.59 rupiah, Philippines 13.18 peso, Brunei 0.34 dollar, Vietnam 5 706.76 dong, Laos 2 083.18 kip, Cambodia 1 003.82 riel, Myanmar 352.42 kyat
Source: textbook p. 16 (xe.com, 18 July 2018)

RM1 has the same value as 8.22 baht. A lollipop that costs RM1 in Malaysia would cost about 8.22 baht in Thailand.

Did you know? Singapore and Brunei both call their money the dollar, and so do the USA and Australia. Always say which country: "Singapore dollar".
What is the currency of Vietnam? Which country uses the rupiah?
Show answerHide answer
Vietnam uses the dong. Indonesia uses the rupiah.

4.7Spending, saving and sharing

Needs are things we must have to live: food, clothes and a place to live. Wants are things that are nice to have but we can live without, such as toys or a new video game.
NeedsWants
Rice, vegetables, waterIce cream, sweets
School uniform, shoesA new football jersey
A house to live inA video game, a toy robot

Use money for needs first. Then, if there is money left, think about wants.

  • Saving means keeping some money for later, in a tabung or a bank account. Savings help in an emergency and help us buy bigger things later.
  • Investing means using money now so that it grows or helps us in the future, for example paying for education.
  • Donating means giving money or things, like clothes, to people who need them, such as flood victims.
Did you know? If you save just RM1 a day, you will have RM30 at the end of a 30-day month. Small savings grow!

4.8Stories and solving problems

Create a story

A number sentence can become a story. For 9 × RM218.50 = RM1 966.50 we can write: "A watch costs RM218.50. A trader buys 9 watches. The total cost is RM1 966.50."

A good story uses all the numbers in the sentence, says what the money is for, and ends with the answer.

Solve the problem in 4 steps

  1. Given: what do you know?
  2. Find: what must you find?
  3. Method: draw a bar model and calculate.
  4. Check: use another way, for example repeated addition.

Example 13: printer and laptop (textbook p. 21)

A printer costs RM429.99. A laptop costs 3 times the price of the printer. What is the price of the laptop?

Bar model: printer RM429.99; laptop is three boxes of RM429.99

3 × RM429.99 = RM1 289.97. Check: RM429.99 + RM429.99 + RM429.99 = RM1 289.97.

Example 14: at the pasar malam

Ayam percik RM6.50 per piece; air tebu RM2.80 per cup

Kak Long buys 2 pieces of ayam percik and 3 cups of air tebu. She pays with a RM50 note. What is her balance?

  1. 2 × RM6.50 = RM13.00
  2. 3 × RM2.80 = RM8.40
  3. RM13.00 + RM8.40 = RM21.40
  4. RM50.00 − RM21.40 = RM28.60
a) Zara has savings of RM369.80. Aisya has RM154.10 less. How much does Aisya have?
b) Tim's mother pays RM2 000 for a cabinet that costs RM1 975. What is her balance? Give it using RM10 and RM5 notes.
Show answerHide answer
a) RM369.80 − RM154.10 = RM215.70
b) RM2 000 − RM1 975 = RM25; for example two RM10 notes and one RM5 note (other answers are possible, e.g. one RM10 and three RM5).

Summary

  • RM1 = 100 sen. Line up the decimal points and write RM in every answer.
  • Total → add. Balance and difference → subtract. Cash in → add, cash out → subtract. Cheaper → subtract, more expensive → add.
  • Multiply: sen first, then ringgit; 100 sen make RM1. × 10, 100, 1 000 moves digits left.
  • Divide: share equally; ÷ 10, 100, 1 000 moves the decimal point left. Check with multiplication.
  • Each country has its own currency: baht (Thailand), rupiah (Indonesia), peso (Philippines), dong (Vietnam), yen (Japan) and more.
  • Spend on needs before wants; save, invest and donate wisely.
  • Solve problems with Given, Find, Method, Check, and draw a bar model.