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Workings

Hint
If we look at all of the clues, each person appears exactly twice.

Answer
Alex had been teaching for 21 years.
Billie had been teaching for 15 years.
Charlie had been teaching for 7 years.

Reasoning
If we look at all of the clues, each person appears exactly twice.

So the total of the three clues gives us two lots of Alex + Billie + Charlie = 36 + 22 + 28 = 86.

So, Alex + Billie + Charlie = 43 years.

In each clue we are given two of the people, so we can use this to find the missing person:

   Charlie and Billie had been teaching for a total of 22 years, which means that Alex must be: 43 – 22 = 21 years.

   Charlie and Alex had been teaching for a total of 28 years, which means that Billie must be: 43 – 28 = 15 years.

   Alex and Billie had been teaching for a total of 36 years, which means that Charlie must be: 43 – 36 = 7 years.

Reasoning With Algebra
Let Alex = A, Billie = B and Charlie = C, then:

[1]   A + B = 36
[2]   C + B = 22
[3]   C + A = 28

If we use [3] – [2] we have:

[4]   A – B = 6

If we use [1] + [4] we have:

   2A = 42
    A = 21

By [1] B = 15. By [3] C = 7.

Workings

Hint

Answer
49 tonnes of chicken feed, 46 tonnes of pig feed and 5 tonnes of cattle feed.

Workings

Hint
Which dog was first, and which was second?

Answer
# Name     Breed
1 Jamie    Dalmatian
2 Sammy    Alsatian
3 Whitney  Great Dane
4 Jimmy    Poodle

Reasoning
(Clue 1) Jamie was first, and (Clue 3) Sammy the Alsatian was second:
   # Name     Breed
   1 Jamie
   2 Sammy    Alsatian
   3
   4

(Clue 4) Whitney was owned before the poodle, leaving Jimmy last:
   # Name     Breed
   1 Jamie
   2 Sammy    Alsatian
   3 Whitney
   4 Jimmy    Poodle

(Clue 2) the Dalmatian was before the Great Dane:
   # Name     Breed
   1 Jamie    Dalmatian
   2 Sammy    Alsatian
   3 Whitney  Great Dane
   4 Jimmy    Poodle

Workings

Hint
Where on Earth can you end up back where you start?

Answer
White.

They were at the north pole and saw a polar bear.