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

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10

If one and a half boys, eat one and a half burgers in one and a half hours.

How many burgers can 9 boys eat in 3 hours?

Replace all '*' with digits 1, 2, 3, 4, 5 and 6 to make below statement true.

* *
x *
=====
* * *

I am an odd number. Take away a letter and I become even. What number am I?

I am a number I am not an odd number I am higher than 90 I am not higher than 100 If you subtract me from 100, you get nothing. What number am I?

Can you arrange four 9's and use at most 2 math symbols, to make the total 100?

What three numbers, none of which is zero, give the same result whether they’re added or multiplied?

Can you make the number 24 by utilizing the numbers 1, 3, 4 and 6? You must use one number only one time and you can use mathematical operation symbols anytime anywhere.

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?