Posts Tagged ‘Maths Olympiad’
How many 3-digit numbers are multiple of 21?
Yes, we can solve this question by counting, but there is another way to solve this type of problem.
First, find the smallest 3-digit number divisible by 21:
- the smallest 3-digit number is 100
- divide 100 by 21 gives 4.76, which rounds up to 5
- so the smallest 3-digit multiple of 21 will be 5 x 21 = 105.
Next, find out the largest 3-digit number divisible by 21:
- the largest 3-digit number is 999
- divide 999 by 21 gives 47.57, which rounds down to 47
- so the largest 3-digit multiple of 21 will be 47 x 21 = 987.
Method 1: The 3-digit multiples of 21 form the arithmetic sequence
5 x 21, 6 x 21, …, 46 x 21, 47 x 21
Hence, the number of 3-digit numbers which are multiples of 21 is 47 – 5 + 1 = 43
Method 2: Find out how many intervals by 21 are between these two numbers.
(987 – 105) ÷ 21 = 42
Hence, the number of multiples of 21 from 105 to 987 inclusively is 42 + 1 = 43.
Now, let’s try this:
How many 3-digit numbers are multiple of 23?
Answer: 39
Power Point: Maths Olympiad-Bases other than Ten
PDF worksheet: MathsOlympiad-Advanced-L19-Bases-other-than-Ten.pdf
Maths Olympiad Book 6 (Chinese)
Posted October 10, 2016
on:Some Maths Olympiad books I found from the web.
Maths Olympiad Book 5 (Chinese)
Posted October 9, 2016
on:Some Maths Olympiad books I found from the web.
Maths Olympiad Book 4 (Chinese)
Posted October 8, 2016
on:Some Maths Olympiad books I found from the web.
Maths Olympiad Book 3 (Chinese)
Posted October 7, 2016
on:Some Maths Olympiad books I found from the web.
This is a tough series question I bumped into in FB. And oh my, it’s Primary 3 question.
Find A in the following series:
24, 36, 72, 90, A
:
:
Maths Olympiad Book 2 (Chinese)
Posted October 6, 2016
on:Some Maths Olympiad books I found from the web.
Maths Olympiad Book 1 (Chinese)
Posted October 5, 2016
on:Some Maths Olympiad books I found from the web.