Brain Teasers and Puzzles 

Workings

Hint
How many days separate the two dates?

Answer
18 days.

Reasoning
There are 140 days between the two dates, and these 140 days are split in the following way:

   4 x Answer | 50 days | Answer

We already know about 50 days, so we have to split the remaining 90 days into the ratio 4:1, which is 72:18.

   72 days | 50 days | 18 days

Workings

Hint
Look at the last letters.

Answer
Steve.

The last letters are in alphabetical order.

Workings

Hint
A little algebra might help.

Answer
¹/₈.

Reasoning
If we convert the question to algebra, we have:
((n^2 + 4) x 2 – 3) x 4 – n = 20

Expanding the brackets and simplifying gives:

(2n^2 + 8 – 3) x 4 – n = 20

    (2n^2 + 5) x 4 – n = 20

         8n^2 + 20 – n = 20

              8n^2 – n = 0 (*)

                8n – 1 = 0

                    8n = 1

                     n = ¹/₈

In the equation marked (*) zero is also a potential solution, but as the question tells us that we "Start with a number larger than 0" we know that n can't be 0, and therefore we can safely divide by n.

Double-Checking
                 ¹/₈
   squared     = ¹/₆₄
   add 4       = 4¹/₆₄
   double      = 8¹/₃₂
   take away 3 = 5¹/₃₂
   times 4     = 20¹/₈

   subtracting ¹/₈ gives 20, as required.

Workings

Hint

Answer