Brain teasers

17th July 1998 at 01:00
Puzzles to test mathematical skills - answers below

Maths challenge

Age 7-9

Ben's numbers

Ben has written a list of different numbers.

The digits of each number add up to 5.

None of the digits is zero.

Here is one of them: 23

Ben has written all the numbers he can think of.

How many different numbers are there in his list?

Maths challenge

Age 9-11

Make five numbers

You need a set of ten cards numbered 0 to 9

Use every card once in each of the following problems.

Arrange them to make:

a. five numbers that are multiples of 3;

b. five numbers that are multiples of 7;

c. five prime numbers.

BRAIN TEASER SOLUTIONS

Ben's numbers:

There are 16 different numbers in Ben's list:

5, 14, 23, 32, 41, 113, 122, 131, 212, 221, 311, 1112, 1121, 1211, 2111, 11111.

Make five numbers:

For example:

a. 12, 39, 45, 60, 78 b. 7, 42, 63, 98, 105 c. 5, 23, 67, 89, 401 There are other solutions.

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