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Logic problems
Textbook: Part 2, pp. 95–96
GoalSolve logic puzzles by thinking, drawing and calculating.
New words
logic · mantiqpattern · qonuniyatguess · taxminchecking · tekshirish
Explanation
In a logic puzzle the answer is not given directly: we find it by thinking. Useful ways: draw a diagram, work backwards (from the end to the start), find a pattern, guess and check. Always put the answer back into the puzzle to check.
Worked examples
On a 100 m path with a tree at both ends and every 10 m: there are 100 : 10 = 10 gaps, so 10 + 1 = 11 trees.
I multiplied my number by 4 and added 6 to get 38. Working backwards: (38 − 6) : 4 = 8.
Class activity
“Logic hour”: groups solve one puzzle in different ways (diagram, working backwards, guess and check) and discuss which way was easier.
Practice
1
I thought of a number, multiplied it by 4, added 6 and got 38. Which number did I think of?
8
2
Five friends meet and each shakes hands once with every other friend. How many handshakes are there in total?
10
3
Each of the 25 pupils in a class goes to a swimming or a drawing club. 14 go swimming and 17 go to drawing. How many pupils go to both clubs?
6
4
On a balance 1 melon equals 3 apples and 1 apple equals 4 apricots. How many apricots equal 1 melon?
12
5
Find the pattern: 3, 6, 12, 24, ... What is the next number?
48
6
A father is 4 times as old as his son, and the difference between their ages is 30 years. How old is the son?
10
7
A 12 m rope must be cut into 3 m pieces. How many cuts are needed?
3