### 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?

# Missing Digits

##### Age 11 to 14 ShortChallenge Level

Answer: K, L, M, N, P are 1, 0, 2, 5, 6.

Working it out by doing the calculation
4$\times$4 = 16, so P must be 6

6$\times$4 + 1 = 25, so N must be 5

5$\times$4 + 2 = 22, so M must be 2

2$\times$4 + 2 = 10, so L must be 0

Now, 0$\times$4 + 1 = 1, so K must be 1.

So K, L, M, N, P are 1, 0, 2, 5, 6.

Using algebra
Suppose we are looking for the number KLMNP, and let KLMNP $=x$.
Then the top number, KLMNP4, is KLMNP0 + 4, which is $10x+4$.
The bottom number, 4KLMNP, is 400 000 + KLMNP, which is $400000+x$.

So $(10x+4)\times4=400000+x$. Solving for $x$,\begin{align}40x+16&=400000+x\\39x+16&=400000\\39x&=399984\\x&=399984\div39=10256\end{align}
So K, L, M, N, P are 1, 0, 2, 5, 6.

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