Skip to main content
### Number and algebra

### Geometry and measure

### Probability and statistics

### Working mathematically

### For younger learners

### Advanced mathematics

# Triangular Clock

Trinni is fascinated by triangular numbers (1, 3, 6, 10, 15, 21, etc.).

She found that she could rearrange the twelve numbers on a clock face so that each adjacent pair added up to a triangular number.

She left the 12 in its usual place; what number did she put where the 6 would usually be?

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.

Or search by topic

Age 11 to 14

ShortChallenge Level

- Problem
- Solutions
- Teachers' Resources

Trinni is fascinated by triangular numbers (1, 3, 6, 10, 15, 21, etc.).

She found that she could rearrange the twelve numbers on a clock face so that each adjacent pair added up to a triangular number.

She left the 12 in its usual place; what number did she put where the 6 would usually be?

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.

This problem is taken from the UKMT Mathematical Challenges.

You can find more short problems, arranged by curriculum topic, in our short problems collection.