Can you find out which number multiplied by itself will give the output as 12345678987654321?

Can anyone tell me a word in the English dictionary which has a silent 'z'?

You are in a room that has three switches and a closed door. The switches control three light bulbs on the other side of the door. Once you open the door, you may never touch the switches again. How can you definitively tell which switch is connected to each of the light bulbs?

What are the next two letters in the following series and why?
W A T N T L I T F S _ _

*Hint: Check Puzzle Title

I am something people love or hate. I change peoples appearances and thoughts. If a person takes care of them self I will go up even higher. To some people I will fool them. To others I am a mystery. Some people might want to try and hide me but I will show. No matter how hard people try I will Never go down. What am I?

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

You can see three almost identical images below. Can you spot the odd one out from them?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?

As you can see that fifteen matches have been used to form an arrangement. What you have to do is remove any six of them to make them ten.

Rearrange the letters in "new door" to make one word.