137
Equations
Textbook: Part 4, lesson 128, pp. 26–27
GoalSolve equations with multiplication and division: unknown factor, dividend and divisor.
New words
factor · ko‘paytuvchidividend · bo‘linuvchidivisor · bo‘luvchiquotient · bo‘linma
Explanation
To find an unknown factor, divide the product by the known factor: x × 7 = 35, x = 35 : 7 = 5. To find an unknown dividend, multiply the quotient by the divisor: x : 7 = 8, x = 8 × 7 = 56. To find an unknown divisor, divide the dividend by the quotient: 25 : x = 5, x = 25 : 5 = 5. In a longer equation, do the known operation first: m + 24 : 6 = 19 → m + 4 = 19 → m = 15.
Worked examples
x : 7 = 8: x = 8 × 7 = 56. Check: 56 : 7 = 8.
45 : 9 + n = 51: 5 + n = 51, n = 51 − 5 = 46.
Class activity
“Which operation?”: children show with hand signs which operation solves each equation: division – hands apart, multiplication – crossed hands, addition/subtraction – one hand up.
Practice
1
x × 7 = 35, x = ?
5
2
x : 7 = 8, x = ?
56
3
25 : x = 5, x = ?
5
4
m + 24 : 6 = 19, m = ?
15
5
172 − 65 − t = 13, t = ?
94
6
A factory assembles 20 cars in two days. How many cars does it assemble in one day?
10