Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

What is the word or phrase?

What has many keys but can’t open a single lock?

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

Consider all the numbers between 1 and 1 million. Among all these numbers, there is something very special about the number 8 and the number 2202. What is it?

If you go to the movies and you're paying, is it cheaper to take one friend to the movies twice, or two friends to the movies at the same time?

How can you take 2 from 5 and leave 4?

Can you make four (4) nines (9) equal 100?

I am lying and I always lie. Tell me whether I am lying or telling the truth.

Find three numbers such that When we multiply three numbers, we will get the prime numbers. The difference between the second and the first number is equal to the third and second.