Mathematical Puzzles 

Workings

Hint
How many miles did I travel?

Answer
I had lost 4 gallons.

Reasoning
I travelled at 50mph for 4 hours, which is 200 miles.

I used 25 gallons every 25 miles, so I used 8 gallons travelling those 200 miles.

I started with 12 gallons and used 8 gallons, so I lost the other 4 gallons.

Workings

Hint
Work out the total number of legs.

Answer
23 children (46 legs).

With 230 ants (1380 legs), 3 puppies (12 legs), and 1 teacher (2 legs).

If we call the number of puppies P, then there were (P + 20) children and 10 x (P + 20) ants, and a single teacher. If we now count the legs, we get:
Puppies:
 P x 4 =  4P

Children:
 (P + 20) x 2 =  2P + 40

Ants:
 10 x (P + 20) x 6 = 60P + 1200

Teacher: 2

A total of 66P + 1242

Giving:

 66P + 1242 = 1440

 66P        = 198

   P        = 3

So there were 3 puppies, hence 23 children.

Workings

Hint
How many chocolates can they eat in one hour?

Answer
2 hours.

Reasoning
In one hour, Alex eats 27 chocolates, Billie eats 12, and Charlie eats 21.

A total of 60 chocolates.

Therefore, 120 chocolates would take 2 hours.

Workings

Hint
There are 12 inches in a foot, and 1,760 yards in a mile.

Answer
Feet in a 20-mile walk.

Reasoning
There are 12 inches in a foot, 3 feet in a yard, and 1,760 yards in a mile:

   square inches in a piece of carpet 15 yards by 5 yards
      (15 x 3 x 12) x (5 x 3 x 12) = 97,200 square inches.

   feet in a 20-mile walk
      20 x 1760 x 3 = 105,600 feet.