Consecutive Numbers

An investigation involving adding and subtracting sets of consecutive numbers. Lots to find out, lots to explore.

Have You Got It?

Can you explain the strategy for winning this game with any target?

Counting Factors

Is there an efficient way to work out how many factors a large number has?

Colossal Sum

Age 11 to 14 ShortChallenge Level

Answer: $0$

$9^1=9$
$9^2=81$ units digit $1$
$9^3=9\times81$
units digit comes from $9\times1=9$
$9^4=9\times9^3$
units digit comes from $9\times9$ so it will be $1$

And so on - units digits go $9,1,9,1,9,1...$

So the last digit of this sum will come from $9+1=10$ - so it will be $0.$

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