Mathematical Puzzles 

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
8.

Workings

Hint
What do the 3 numbers add and multiply to give so far?

Answer
$0.50.

The three prices add to 1.50 + 3.00 + 4.00 = 8.50.

The three prices multiply to 1.50 x 3.00 x 4.00 = 18.00.

You might be able to see that adding another 0.50 will take the total to 9.00, and multiplying by another 0.50 will take the product to 9.00.

The answer can also be found using algebra. If we call the missing price P, we have:
1.50 + 3.00 + 4.00 + P = 1.50 x 3.00 x 4.00 x P

    8.50 + P = 18.00 x P

        8.50 = 18.00 x P - P

        8.50 = 17.00 x P

8.50 ÷ 17.00 = P

           P = 0.50.

Workings

Hint

Answer
The bottle cost 35 pence and the straw cost 25 pence.