39
Word problems and consolidation
Textbook: Part 1, lesson 38, pp. 80–81
GoalSolving problems with expressions and equations; inverse problems.
New words
problem · masalainverse problem · teskari masalaexpression · ifodacondition (given facts) · shart
Explanation
To solve a problem we read the condition, write it briefly, choose the operation, write an expression and check. One table gives three problems: there were 45, 5 were added, now there are 50. In inverse problems the unknown changes place.
Worked examples
45 + 5 = 50; 45 + ? = 50 → 50 − 45 = 5; ? + 5 = 50 → 50 − 5 = 45.
Add the sum of 16 and 18 to 12: 12 + (16 + 18) = 12 + 34 = 46.
Class activity
“Problem workshop”: pairs make three inverse problems from a table and pass them to another pair to solve.
Practice
1
(45 + 12) − 17 = ?
40
2
52 + x = 67 + 14. x = ?
29
3
(58 + 27) − 38 = ?
47
4
Last year a hospital did 17 operations and this year 6 more. How many in the two years?
40