The Professor's Riddles

Alfred and Roland have been hired by a farm to sow flower seeds. They've been assigned a 10-acre plot of land and split it in half so they can work independently. Roland starts from the east and Alfred from the west.

Alfred can plow the land at a rate of 20 minutes per acre. Roland takes 40 minutes to plow, but sows seeds at three times the speed Alfred does.

If sowing seeds on the 10-acre plot pays $100, how much of that money should go to Roland?

While walking through a market on holiday, you notice a small stand selling cameras. A camera and case set is selling for £310. The merchant tells you that the camera costs £300 more than the case itself and that the case costs the price of the set minus the cost of the camera.
You decide to just buy the case without the camera. You hand the merchant £100. How much change should you get back?

Five cats can catch five mice in five minutes.

With that in mind, how many cats does it take to catch 100 mice in 100 minutes?

A train with a length of 100m takes 30 seconds to travel over a 400m bridge.

Assuming that the train's speed is constant, how many kilometres per hour is it travelling at?

Arrange 9 unique numbers between 1 and 51 so that every vertical, horizontal and diagonal line of numbers crossing through the middle square has the same sum.

Arrange the numbers so that they yield the highest possible sum.

What number occupies the middle square?

A glass jar holds a single germ. After one minute, the germ splits into two germs. One minute after that, the two germs each split again, forming a total of four germs. Continuing at this rate, a single germ can multiply to fill the whole jar in exactly one hour.

Knowing this, how long in minutes would it take to fill the jar if you had started with two germs?

Ten candles stand burning in a dining room. A strong breeze blows in through an open window and extinguishes two of them. Checking back in on the candles later, you see that one more candle has gone out. To make sure no more flames go out, you shut the window. Assuming the wind doesn't extinguish any more candles, how many candles do you have left in the end?

Three boys are talking about how many sweets they each have.

A: B has the most!
B: If C gave me one sweet, I'd have twice as many as A does.
C: It'd be better if B gave me two sweets. Then we'd all have the same amount!

How many sweets are there in total?