Which is the rope you never skip with?

I am looking for a word that change both gender and number when i add the letter 'S'.

What Word am I Looking For ?

What is the word or phrase?

In case you were starting to feel confident, this one was meant for third graders in Vietnam. The answer is 66, but we don't blame you for scratching your head about how they got there.

You Throw The Outside, Cook The Inside
Eat The Outside, Throw The Inside.

What Is It?

Find a 9-digit number, which you will gradually round off starting with units, then tenth, hundred etc., until you get to the last numeral, which you do not round off. The rounding alternates (up, down, up ...). After rounding off 8 times, the final number is 500000000. The original number is commensurable by 6 and 7, all the numbers from 1 to 9 are used, and after rounding four times the sum of the not-rounded numerals equals 24.

If in a car race, the man who came two places in front of the last man finished one ahead of the man who came fifth, how many contestants were there?

How many pluses should we put between the digits of 987654321 to get a total of 99, and where?

The chance of Mr John winning the lottery is 10%. All participants lined up and Mr John is 4th in the row. The first three participants lose the lottery.

What is the chance of Mr John now?

The average age of 10 members of a committee is the same as it was 4 years ago, because an old member has been replaced by a young member. Find how much younger is the new member ?