Quickly Solve this riddle

7 - 4 + 3 * 0 + 1 = ?

Using four sevens (7) and a one (1) create the number 100. Except for the five numerals, you can use the usual mathematical operations (+, -, x, :), root and brackets ()

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

Can you arrange four 9's and use at most 2 math symbols, to make the total 100?

A high school has a strange principal. On the first day, he has his students perform an odd opening day ceremony:

There are one thousand lockers and one thousand students in the school. The principal asks the first student to go to every locker and open it. Then he has the second student go to every second locker and close it. The third goes to every third locker and, if it is closed, he opens it, and if it is open, he closes it. The fourth student does this to every fourth locker, and so on. After the process is completed with the thousandth student, how many lockers are open?

The sum of a mother, her baby and her dog's weight is 170 Kg. How much does the baby weigh if the mother weighs 100 kg more than the combined weight of the baby and the dog, and the dog weighs 60 per cent less than the baby?

What's a single-digit number with no value?

Find the value of "?" in the ball picture Riddle below:

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

Can you find out the smallest number that can be conveyed as the sum of three squares in three unique ways?