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

A four-digit number (not beginning with 0) can be represented by ABCD. There is one number such that ABCD=A^B*C^D, where A^B means A raised to the B power. Can you find it?

How many triangles are there in the picture below?

You are given a cube that is made with the help of 10x10x10 smaller cubes summing up to a total of 1000 smaller cubes. You are asked to take off one layer of the cubes.
How many remain now?

Double it and multiply it by 4. Then divide it by 8 and you’ll have it once more. What number is it?

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

What is the largest number you can write with just 3 digits?

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

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

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?