Medium Puzzles 

Workings

Hint
How many rooms can Alex clear in 36 hours?

Answer
12 hours.

Reasoning
In 36 hours, Alex could empty 2 lots of bookshelves, Billie could also empty 2 lots of bookshelves, and Drew could refill 1 lot of bookshelves.

So, 2 + 2 – 1 = 3 lots of bookshelves in 36 hours. Which is 12 hours for one lot of bookshelves.

Alternative Reasoning
Alex and Billie can each empty ¹/₁₈ of the bookshelves in 1 hour, but Drew will refill ¹/₃₆ of the bookshelves in one hour.

So in one hour we have ¹/₁₈ + ¹/₁₈ – ¹/₃₆ = ¹/₁₂.

So it would take 12 hours to empty the bookshelves.

Workings

Hint
What's a mathematical way to describe placing a 9 at the beginning?

Answer
23,076.

Reasoning
Placing the 9 at the beginning is equivalent to adding 900,000 (for example, 12,345 + 900,000 becomes 912,345).

Placing the 9 at the end is equivalent to multiplying by 10 and adding 9 (for example, 12,345 x 10 + 9 becomes 123,459).

Let's call the unknown number k, and we know that one of these numbers is 4 times the other, so:

 k + 900,000 = 4 x (10k + 9)

 k + 900,000 = 40k + 36

900,000 – 36 = 40k – k

     899,964 = 39k

899,964 ÷ 39 = k

Therefore, k = 23,076.

Double-Checking
923,076 = 4 x 230,769.

Workings

Hint
The first letter is M.

Answer
Mouse.

Reasoning
My first is in camel, and in hamster = AEM
My second is in otter, but not in ferret = O
My third is in mustang, but not in horse = AGMNTU
My fourth is in snake, and in asp = AS
My last is in tiger, and in panther = ERT

Workings

Hint
The longest word is the answer to 'Frozen atmospheric vapour falling to earth'.

Answers
Snowing, sowing, swing, sing, sin, in, I.
   snowing – frozen atmospheric vapour falling to earth
    sowing – scattering on the earth
     swing – cause to oscillate
      sing – to utter musical sounds with the voice
       sin – the breaking of divine law
        in – expressing position within limits of space and time
         I – the subject of self-consciousness