6
Review: formulas
Textbook: Part 1, lesson 6, pp. 19–21
GoalReview the price–quantity–cost formulas and the formulas for perimeter, area and volume.
New words
formula · formulaprice · narxquantity · miqdorcost (value) · qiymat
Explanation
A formula is a rule linking quantities, written with letters. With cost C, price a and quantity n: C = a × n, a = C : n, n = C : a. We put numbers in place of the letters and find the unknown. For a rectangle P = (a + b) × 2 and area S = a × b; the volume of a cuboid is V = a × b × c.
Worked examples
If a = 4 500 sum and n = 8, then C = 4 500 × 8 = 36 000 sum.
If C = 84 000 sum and n = 12, then a = 84 000 : 12 = 7 000 sum.
Class activity
“Market game”: one child is the seller, another the buyer. The seller states a price and a quantity and the buyer works out the cost with the formula; then they swap.
Practice
1
One kilogram of grapes costs 6 500 sum. How many sum do 12 kg cost?
78000
2
How many notebooks at 8 000 sum each can be bought for 96 000 sum?
12
3
15 identical books cost 165 000 sum. What is the price of one book in sum?
11000
4
A box is 12 cm long, 5 cm wide and 4 cm high. What is its volume in cm³?
240