Mathematical Puzzles 

Workings

Hint
Don't forget the extra 9's in 90, 91, etc.

Answer
300.

Reasoning
Start with: 9, 19, 29, 39, 49, 59, 69, 79, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 – which is 20 9's.

We then repeat this for 100, 200, 300, up to 900 – which is 200 9's.

But from 900 to 999 we have an extra 100 9's as each starts with a 9.

So the total is 300.

Workings

Hint
It doesn't matter how far it was to Manchester, so you can use any distance.

Answer
Billie.

Reasoning
If we call the one way distance T, we know that:

On the way there, Alex drove 90 miles, and Billie drove (T – 90) miles.

On the way back, Alex drove (T – 100) miles, and Billie drove 100 miles.

So, in total, both ways:

   Alex drove 90 + (T – 100)
      = T – 10

   Billie drove (T – 90) + 100
      = T + 10

Therefore, Billie drove 20 miles more than Alex.

Workings

Hint
How many minutes are there between 2:00 and 7:00?

Answer
65 minutes.

Reasoning



We need to break down the five hours in the following way:

3 x Answer minutes past two o'clock 40 minutes Answer minutes before seven o'clock
Why? It is now Answer minutes before seven o'clock, and then we have the 40 minutes before that, and the remaining time was 3 x Answer minutes past two o'clock.

So, five hours = 5 x 60 = 300 minutes. We already know about the 40 minutes, so we have to share the remaining 260 minutes in the ratio 3:1, which gives 195:65 minutes. Or using algebra 4 x Answer = 300 – 40, so Answer = 65 minutes.

Therefore, the five hours is made up of:

195 minutes past two o'clock 40 minutes 65 minutes before seven o'clock
So, it's currently 65 minutes before 7:00 = 5:55.

Double-Checking
It is now 65 minutes before seven o'clock = 5:55, so 40 minutes ago it was 5:15 – which is 195 minutes after 2:00, as required (as 65 x 3 = 195).

Workings

Hint
Start by going up.

Answer
The largest total that can be made is 8.