Can you find the missing piece of the Porsche?

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

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

I am a seven-letter word but if you remove four of my letters I will have one left. What word am I?

In a football game, Christina defeated Teresa by 2 - 0 but no man from either side scored. How can this be possible?

Can you replace the question mark with the correct letter?

6 + 6 + 6 = N
7 + 7 + 7 = E
8 + 8 + 8 = R
0 + 0 + 0 = ?

f you were running a race, and you passed the person in 2nd place, what place would you be in now?

Three men in a cafe order a meal the total cost of which is $15. They each contribute $5. The waiter takes the money to the chef who recognises the three as friends and asks the waiter to return $5 to the men.

The waiter is not only poor at mathematics but dishonest and instead of going to the trouble of splitting the $5 between the three he simply gives them $1 each and pockets the remaining $2 for himself.

Now, each of the men effectively paid $4, the total paid is therefore $12. Add the $2 in the waiters pocket and this comes to $14. Where has the other $1 gone from the original $15?

I come in different shapes and sizes.
Parts of me are curved, other parts are straight.
You can put me anywhere you like,
but there is only one right place for me.
What am I?

By including only four matchsticks in below picture, you have to make "Four Triangles And Two Squares"