Random Puzzles 

Workings

Hint
Try starting with the cat.

Answer
He can take the cat across first and then come back.

Then take the dog across and bring the cat back.

Then take the mouse across and come back.

Finally, take the cat across again.

Workings

Hint
Start on any square, and see how far you get.

Answer
Start from the 2U in the bottom right-hand corner.

Workings

Hint
There are two different methods, one involves a cube root, and the other doesn't require a calculator.

Answer
9 x 11 x 13.

Reasoning #1
We're after three numbers that multiply together, so a good place to start is the cube root of 1,287, which is roughly 10.88.

Let's try dividing by the closest odd number to 10.88:

   1287 ÷ 11 = 117

We're now after whole divisors of 117. Trying the odd numbers either side of 11 might work.

Trying either 9 or 13 gives the answer:

   9 x 11 x 13 = 1,287

Trying the closest odd number to the cube root always works, and the other two numbers are the odd numbers either side.

Reasoning #2
We after three numbers that multiply together, but none of these can end in 5 (otherwise our answer would end in 0 or 5).

So, they can only end in 7, 9, 1 (e.g. 87, 89, 91), or 9, 1, 3 (e.g. 89, 91, 93).

However, if they ended in 7, 9, 1, the answer would end in 3 (because 7 x 9 x 1 = 63).

Therefore, they end in 9, 1, and 3 (because 9 x 1 x 3 = 27).

The first numbers we can try are 9, 11, 13:

   = 9 x 11 x 13
   = 99 x 13
   = 100 x 13 - 13
   = 1300 - 13
   = 1,287

A calculator is not required!

Workings

Hint
Read the question carefully.

Answer
56 cubic feet (= 4 x 7 x 2).

We usually ask how much earth there is in a hole, which of course there is none!