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Harder problems and logic
Textbook Part 3, pp. 42–43
GoalSolve problems with several addends the easy way; solve logic problems by reasoning.
New words
logic problem · mantiqiy masalareasoning · fikrlashclosed curve · yopiq egri chiziq
Explanation
Logic problems are solved by reasoning rather than calculating. For example: “There are 2 more squares than circles, and 1 fewer circle than triangles” — pick one amount first and work out the rest from it.
Worked examples
At an open lesson three pupils recited poems for 3, 2 and 4 minutes: 3 + 2 + 4 = 9 minutes.
If there are 3 triangles: 2 circles (1 fewer) and 4 squares (2 more than circles).
Class activity
Word puzzle: in PAXTA, SODDA and DASTA the same letters are replaced by the same shapes. Children work out which shape stands for which letter.
Practice
1
The easy way: 15 + 8 + 5 + 2
30
2
36 + 12 − 8 = ?
40
3
There are 4 triangles. Circles are 1 fewer, and squares are 2 more than circles. How many squares?
5
4
Draw a red straight line and a blue closed curve that does not cross it. Is it possible?
Yes — draw the curve entirely on one side of the line