Complete the following series. It.s very logical:

1, 4, 5, 6, 7, 9, 11, __?

I have four wings but can't fly.
I express no emotions.
I am found on the exact spot every time you look.
I keep toiling away with a little sound.

Do you know what am I?

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?

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

You have three orange, two pink and five purple balls in the drawer beside your bed. There is no electricity and the room is entirely dark. How many balls must you take out to ensure at least one ball of each colour at least?

In a concert, Christina is performing a dance show with her group.
At 10:00, she and her crew were dancing in an absolutely straight line. At that time Christina was standing in 4th position from both the front and back end of the row.

What was the size of her crew?

Remove two matchsticks to make the below equation correct.

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

My first is in chocolate but not in ham. My second is in cake and also in jam. My third at tea time is easily found. Altogether, this is a friend who is often around. What is it?

what does this picture(rebus) riddle means ?