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Worked examples
Twenty questions from this topic with their answer and the method used. Start the quiz above to practise with other variants.
A 12-hour clock shows 10. What will it show 16 hours later?
Answer 2
(10 + 16) mod 12 = 2; 0 → 12.
What is binary 10001 in base 10?
Answer 17
10001₂ = 17₁₀.
Add 6 each time: 10, 16, 22, … What comes next?
Answer 28
22 + 6 = 28.
In a group of 9 people, each shakes hands with every other person once. How many handshakes?
Answer 36
9 × 8 ÷ 2 = 36.
How many cells are in a grid with 2 rows and 42 columns?
Answer 84
2 × 42 = 84.
Objects are placed in 44 boxes. What is the minimum number that guarantees at least 2 in one box?
Answer 45
44 + 1 = 45.
What is the remainder when 143 is divided by 7?
Answer 3
143 = 7 × 20 + 3.
Double each time: 18, 36, 72, … What comes next?
Answer 144
72 × 2 = 144.
A 12-hour clock shows 2. What will it show 16 hours later?
Answer 6
(2 + 16) mod 12 = 6; 0 → 12.
What is binary 110011 in base 10?
Answer 51
110011₂ = 51₁₀.
Add 6 each time: 18, 24, 30, … What comes next?
Answer 36
30 + 6 = 36.
In a group of 12 people, each shakes hands with every other person once. How many handshakes?
Answer 66
12 × 11 ÷ 2 = 66.
How many cells are in a grid with 2 rows and 43 columns?
Answer 86
2 × 43 = 86.
Objects are placed in 39 boxes. What is the minimum number that guarantees at least 2 in one box?
Answer 40
39 + 1 = 40.
What is the remainder when 276 is divided by 7?
Answer 3
276 = 7 × 39 + 3.
Double each time: 46, 92, 184, … What comes next?
Answer 368
184 × 2 = 368.
A 12-hour clock shows 4. What will it show 16 hours later?
Answer 8
(4 + 16) mod 12 = 8; 0 → 12.
What is binary 10000 in base 10?
Answer 16
10000₂ = 16₁₀.
Add 6 each time: 27, 33, 39, … What comes next?
Answer 45
39 + 6 = 45.
In a group of 22 people, each shakes hands with every other person once. How many handshakes?
Answer 231
22 × 21 ÷ 2 = 231.