Random Puzzles 

Workings

Hint
You can either fix the distance rowed and see what numbers work, or you can fix the number of hours.

Answer
12 miles.

In the morning, rowing at 2 miles per hour, they rowed for 6 hours. In the afternoon, rowing at 4 miles per hour, they rowed for 3 hours.

There are a number of ways of working this out, and here are two of them:

Method 1
If we assume the distance the rowed upstream to be D miles, we know the morning took (D ÷ 2) hours, and the afternoon took (D ÷ 4) hours, with a difference of 3 hours. So:
 D   D
 - – - = 3
 2   4

Multiplying throughout by 4 gives:

 2D – D = 12

So:

 D = 12 miles

They rowed 12 miles upstream.

Method 2
If we assume they rowed for H hours upstream, we know they travelled H x 2 miles in the morning. In the afternoon, they rowed for (H – 3) hours, and travelled (H – 3) x 4 miles. We know these distances are the same, so:

 2H = (H – 3) x 4

Giving:

 2H = 4H – 12

Rearranging gives:

 12 = 2H

So:

 H = 6 hours

They rowed for 6 hours upstream at 2 miles per hour, which is a total of 12 miles.

Workings

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

Answer
Start from the 1L on the fifth row down and second column across.

Workings

Hint
Don't let this one melt your brain.

Answer
This puzzle is a classic paradox.

You can wrangle with the logic for hours and never reach an absolute conclusion.

Workings

Hint
You have to highlight three numbers.

Answer
6 + 1 + 12 = 19.

The puzzle didn't ask for three digits to be highlighted!