Worksheets › Class 8 › Number Play: Thinking Puzzles
Class 8 · Computational Thinking and AI worksheetNumber Play: Thinking Puzzles
CBSE Computational Thinking and AI. Divisibility machines and rules, digit puzzles, remainders and days of the week, counting multiples, age and switch puzzles, a remainder game. Every sheet has 20 questions in three sections and an answer key, and the questions change every time.
Sample questions
Real questions from this chapter, as the app sets them. Tap Answer to see the answer and working.
Section A · multiple choice
- 1.
A number is divisible by 9 when:
- it is odd
- its last two digits make a multiple of 9
- its last digit is 9
- the sum of its digits is divisible by 9
Answer
(d) the sum of its digits is divisible by 9
- 2.
A panel has three bulbs. Bulb A glows when the number entered is divisible by 7, bulb B when it is divisible by 10, and bulb C when it is divisible by 11. Which bulbs glow when 166 is entered?
- A and C
- B and C
- None of them
- A and B
Answer
(c) None of them
166 ÷ 7 leaves 5; 166 ÷ 10 leaves 6; 166 ÷ 11 leaves 1
- 3.
Using six of the digits 9, 1, 8, 2, 0, 3, 5 once each, what is the largest 6-digit number divisible by 9?
- 985,320
- 985,321
- 985,302
- 985,311
Answer
(a) 985,320
drop the digit that makes the digit sum a multiple of 9; arrange the rest from largest to smallest
Section B · short answer
- 4.
Why does the digit-sum test work for 9?
Answer
Each power of 10 is 1 more than a multiple of 9, so a number and its digit sum leave the same remainder on division by 9.
- 5.
A panel has three bulbs. Bulb A glows when the number entered is divisible by 7, bulb B when it is divisible by 6, and bulb C when it is divisible by 10. Which bulbs glow when 32 is entered? Write the letters, or None.
Answer
None
32 ÷ 7 leaves 4; 32 ÷ 6 leaves 2; 32 ÷ 10 leaves 2
Section C · long answer
- 6.
The numbers 4, 20, 29, 33, 34, 37, 44, 51, 53, 54 are sorted into boxes: multiples of 4 go into Box 1 and multiples of 5 into Box 2; a multiple of both goes into both boxes. How many numbers go into (a) Box 1 (b) Box 2 (c) both boxes (d) neither box?
Answer
(a) 3; (b) 1; (c) 1; (d) 7
Box 1: 4, 20, 44; Box 2: 20
Fresh sheets for your child
In the app, every Number Play: Thinking Puzzles sheet is new: the app remembers the questions your child has already had and leaves them out. Print the sheet as a PDF, or use notebook mode and write the answers in a notebook.
Coming soon for Android and iPhone.