162
Logic puzzles
Textbook: Part 4, pp. 77–78
GoalLogic puzzles: finding patterns, listing all options, trick problems.
New words
logic puzzle · mantiqiy topshiriqpattern · qonuniyatoption · variantpair · juftlik
Explanation
In a logic puzzle we read carefully, draw a picture and list all options in order. In 6, 9, 8, 12, 10, 15 the changes are +3, −1, +4, −2, +5 – the next is −3, so 12. If we cut a 20 m rope into 5 m pieces we get 4 pieces, but only 3 cuts are needed: 20 : 5 − 1 = 3.
Worked examples
School breakfast has 3 kinds of porridge and 3 kinds of drink: 3 × 3 = 9 pairs.
Two people plant 2 rows in 2 hours: one person plants 1 row in 2 hours. In 4 hours one person plants 2 rows, so 2 people are enough for 4 rows.
Class activity
“Logic corner”: each group gets one puzzle (a pattern, a combination or a trick problem). The group explains its solution with a picture or table; other groups ask questions.
Practice
1
6, 9, 8, 12, 10, 15, … What is the next number?
12
2
Two people plant 2 rows of seeds in 2 hours. How many people plant 4 rows in 4 hours?
2
3
A banner is 8 m long and 2 m is cut off each minute. How many minutes are needed to cut it all into 2 m pieces?
3
4
A sports book has 200 pages. 50 leaves are 9 mm thick. How thick is the book in millimetres? (1 leaf = 2 pages)
18
5
One tier of a steamer holds 8 dumplings and each steamer has 4 tiers. How many dumplings cook at once in 2 steamers?
64
6
School breakfast has 3 kinds of porridge and 3 kinds of drink. How many different pairs can be chosen?
9