140
Year review: equations, word problems and movement
Textbook: Part 4, lesson 140, pp. 93–94
GoalYear review: equations, multi-step word problems and movement problems.
New words
equation · tenglamaroot · ildizspeed · tezlikdistance · masofa
Explanation
To solve an equation we find the unknown addend, subtrahend, factor or divisor with the inverse operation. To check the root we put it back in the equation. In movement problems s = v × t, v = s : t, t = s : v. In a multi-step problem we write down what we are finding at each step.
Worked examples
(y − 45) × 6 = 300. y − 45 = 300 : 6 = 50, y = 50 + 45 = 95. Check: (95 − 45) × 6 = 300.
A train covered about 300 km from Tashkent to Samarkand in 4 hours. Its speed is 300 : 4 = 75 km/h.
Class activity
“Equation master”: one child thinks of a number and says an equation (“I multiplied my number by 8 and subtracted 56 and got 240”). The others write the equation, find the root and check it.
Practice
1
Find the root of the equation (y − 45) × 6 = 300.
95
2
A train covered 300 km in 4 hours. What is its speed in km/h?
75
3
How many hours does a bus travelling at 60 km/h need for 420 km?
7
4
The first store has 240 kg of apples. The second has 3 times less than the first, and the third has 20 kg more than the second. How many kg of apples are in all three stores?
420
5
Find the root of the equation x × 8 − 56 = 240.
37