#### You may also like ### Days and Dates

Investigate how you can work out what day of the week your birthday will be on next year, and the year after... Think of a number, add one, double it, take away 3, add the number you first thought of, add 7, divide by 3 and take away the number you first thought of. You should now be left with 2. How do I know? ### How Many Miles to Go?

How many more miles must the car travel before the numbers on the milometer and the trip meter contain the same digits in the same order?

##### Age 11 to 14 Challenge Level:

This is what happens, only twisted so that you know what's going on.

The friend picks three consecutive numbers, $x, x+1,$ and $x+2$ where $x \leq 58$.

He/she then picks a number $3n$, where $n \leq 33$ and tells you what it is.

Adding the 4 numbers gives $3x + 3 + 3n = 3(x + 1 + n)$.

Multiplying by 67 gives the number $201(x + 1 + n)$.

We know $x + 1 + n \leq 58 + 1 + 33 = 92$.

So the 2 digit number is 1 times $(x + 1 + n)$ and the rest is $200(x + 1 + n)$ which is 200 times the 2 digit number, so you double the 2 digit number to get the remaining digits.

You know what $n$ is, so subtract $n$ and 1 from the 2 digit number to get $x$.

From Ian Green, Age 13 Coopers Company and Coburn School, Upminster, Essex.