Use only one mathematical symbol and all numbers (0-9) to get a sum of 99

What has a ring but no finger?

I noticed one of the words in the oxford dictionary is spelled incorrectly. What about you?

Which five letter word can be added at the end of below word to form a
valid word?

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When I get multiplied by any number, the sum of the figures in the product is always me. What am I?

Can you think of any three-dimensional shape that comprises of exactly two surfaces?

I look flat, but I am deep. Hidden realms I shelter. Lives I take, but the food I offer. At times I am beautiful. I can be calm, angry, and turbulent. I have no heart but offer pleasure as well as death. No man can own me, yet I encompass what all men must have. What am I?

How many letters are in the alphabet?

Identify Me

Hint1: I am a god
Hint 2: I am a planet
Hint 3: measurer of heat

Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?