Some explanation on the answer Yodha already gave.

The product of the number of chickens and the number of days stays the same, which leads to the following calculations:

C*D = (C-75)*(D+20) = (C+100)*(D-15)
C*D = C*D+20C-75D-1500 = C*D-15C+100D-1500
0 = 20C-75D-1500 = -15C+100D-1500

60C = 225D+4500
60C = 400D-6000

225D+4500 = 400D-6000
175D = 10500
D = 10500/175 = 60
C = 225 + 75
= 400 – 100
= 300

It is not clear what you want us to solve?
Please add more information so we can help you solve your problem.
And if you already have a solution, please let us know.
If we know the solution we can find the question in the text you supplied.

John and his wife are home 10 minutes earlier than normal.
This means that John meets his wife 5 minutes earlier (10 two ways = 2 * 5 one way)
So they meet at 5 minutes before 6.
John walked 55 minutes before he meets his wife.

This is the classic Monty Hall problem.
His chances of winning are 1/3 when he stays with his choice and 2/3 when he switches.

Let Jason do the tossing. He doesn’t know if or how the coin is loaded, so he also doesn’t know how to toss the coin to favor on of the sides.

Toss the coin N times (where N is even). Count the heads in the odd tosses for John and in the even tosses for Jacob. The one who has the greatest number of heads wins.

For the variation just multiply the number for John with a factor x (x>1) so his chance of winning the game increases.
Unfortunately I don’t have time to calculate the relation between x and p.

To solve this it is easier to calculate in minutes.
Suppose it is M minutes after 12 (M = h*60 + m).
In the mirror it will look like 720 – M (720=12*60).
He arrives at school at M + 20.
It looks like it is 150 (2.5*60) minutes after he left:
720 – M + 150 = M + 20
2M = 850
M = 425 = 7*60 + 5

The time he left it was 7:05 but in the mirror it looked like 4:55.
When he arrived at school it was 7:25, two and a half hours after 4:55.

None of those.
It looks like they are using the solfege note scale (https://en.wikipedia.org/wiki/Solf%C3%A8ge#Fixed_do_solf%C3%A8ge) but after La there is Si and none of the names start with Si.

One of the possible solutions is this

The blue squares should be placed like this or mirrored.
And of course you can swap the four other colours.

There are two options.
The butler because on a Sunday there will be no mail delivery. But it could be that he didn’t have time to fetch the mail on Saturday.
The cook because he was preparing lunch in the evening. He should be preparing dinner. But it could be that he was preparing lunch for Monday afternoon.

It is also strange that the gardener was pruning the hedges after 5 pm but I am no gardener.

TWENTY NINE