Discover Mathematics P5: Term 1, Unit 6, Lessons 1–4
GoalTurn a story into a numerical expression, using parentheses where needed, and work out its value.
New words
sum · the result of addingtwice · two times as muchtotal · everything added together
Explanation
To write an expression for a story, split the story into parts and write each part as numbers. Then join the parts with the sign the story tells you. If a part must be worked out before the next step, put it in parentheses. “3 packs at 8 LE and a ruler at 5 LE” is 3 × 8 + 5, because the multiplication comes first anyway. “Two friends each pay for a sandwich (12 LE) and a juice (6 LE)” needs parentheses: 2 × (12 + 6), because the price of one friend’s meal is added before we multiply by 2.
Story
Expression
Value
3 packs at 8 LE, plus a 5 LE ruler
3 × 8 + 5
29
2 meals of 12 LE and 6 LE
2 × (12 + 6)
36
Worked examples
Youssef buys 3 packs of pencils at 8 LE each and a ruler for 5 LE. Expression: 3 × 8 + 5 = 24 + 5 = 29 LE.
Two friends each buy a sandwich for 12 LE and a juice for 6 LE. Expression: 2 × (12 + 6) = 2 × 18 = 36 LE.
A tray holds 24 eggs and 6 are broken. The rest are packed in boxes of 6. Expression: (24 − 6) ÷ 6 = 18 ÷ 6 = 3 boxes.
Class activity
Story cards. The grown-up tells a short shopping story (for example “I buy 4 bottles of water at 5 LE and one bread at 3 LE”). The child writes the expression, works it out and says the answer in a sentence. Then the child makes up a story with parentheses for the grown-up to turn into an expression.
Practice
1
A shop has 5 boxes with 12 oranges each, and 8 oranges are bad. Write an expression and find how many good oranges.
5 × 12 − 8 = 60 − 8 = 52.
2
Salma has 50 LE and buys 4 notebooks at 7.5 LE each. Write an expression for the money left.
50 − 4 × 7.5 = 50 − 30 = 20 LE.
3
Mina buys 2 kg of rice at 18 LE per kg and 3 kg of lentils at 22 LE per kg. Write an expression and find the total.
2 × 18 + 3 × 22 = 36 + 66 = 102 LE.
4
Write “twice the sum of 9 and 6” as an expression and find its value.
2 × (9 + 6) = 2 × 15 = 30.
5
Make up a story for (30 + 18) ÷ 4 and find its value.
For example: 30 story books and 18 comics are shared equally among 4 shelves. (30 + 18) ÷ 4 = 48 ÷ 4 = 12 books on each shelf.
