26
Practical tasks
Textbook: Part 1, lesson 26, pp. 81–83
GoalPractical tasks on comparing costs, saving money and the area of paper needed to wrap a box.
New words
saving · tejashexpense · xarajatcomparing · solishtirishface · yoq
Explanation
To compare two options we find the cost of both under the same conditions (for example, for the same number of trips) and subtract: the difference is the saving. To wrap a box we add the areas of all six faces; opposite faces are equal, so S = 2 × (a × b + a × c + b × c).
Worked examples
One trip costs 1 600 sum and a day ticket 5 000 sum. For 4 trips a day: 1 600 × 4 = 6 400, with the ticket 5 000 – you save 1 400 sum.
A box 30 × 20 × 10 cm: S = 2 × (600 + 300 + 200) = 2 200 cm² of paper is needed.
Class activity
“Which is cheaper?”: children compare two shopping offers (for example single items and a bundle) and prove which one is better value.
Practice
1
One trip costs 1 600 sum and a day ticket 5 000 sum. With 4 trips a day, how many sum a day does the ticket save?
1400
2
How many sum is this saving over 20 school days?
28000
3
Offer: four pens for the price of three. One pen costs 3 500 sum. How many sum are saved if you take four?
3500
4
A box is 30 cm × 20 cm × 10 cm. How many cm² of paper are needed to wrap it (no overlaps)?
2200