What is black when you buy it, red when you use it, and gray when you throw it away?

Can you name four days which start with the letter 'T'?

Three cars are driving on a track that forms a perfect circle and is wide enough that multiple cars can pass anytime. The car that is leading in the race right now is driving at 55 MPH and the car that is trailing at the last is going at 45 MPH. The car that is in the middle is somewhere between these two speeds.
Right now, you can assume that there is a distance of x miles between the leading car and the middle car and x miles between the middle car and the last car and also, x is not equal to 0 or 1.
The cars maintain their speed till the leading car catches up with the last car and then every car stops. In this scenario, do you think of any point when the distance between any two pairs will again be x miles i.e. the pairs will be x distance apart at the same time ?

Three logicians went to bar for having a drink. The bar person asks the logicians "Do they all want to have the drink?". The first logician replied, " I don't know". The second logician replied, " I don't know". What is the reply of the last logician?

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

What does this rebus mean?

O
N
C
E
TIME

What can run but never walks, has a mouth but never talks, has a head but never weeps, has a bed but never sleeps?

I am never scared but became petrified and can’t live in a house but would die to make one. What am I?

What word is identified by the below rebus?

Your Your Your Your Your
Your Your Your Your Your

Christina is older than Kareena and Karishma. Katrina is older than Karishma and younger than Kareena. If Kareena has a brother named John, who is older than Christina, who's the youngest?