How many sides does a circle have?

Can you spot what's wrong with the following sentence?

PETER WAS ANGRY AT
HIMSELF BECAUSE HE
ACCIDENTALLY LEFT THE
THE KEYS TO HIS CAR
AT HIS FRIEND'S HOUSE.

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

I am a five-letter word and comprises two different vowels and three same consonants. I am so strong that I can spoil your entire work.

Can you find out who am I?

I know a nine-letter word having only one vowel.
Do you ?

If an electric train is travelling south, then which way is the smoke going?

If,

A = 1

B = 2

C = 3

...

...

Z = 26.

Based on above rule, you need to find an eleven letter word whose letter sum is equal to 52.

Before Mount Everest was discovered, what was the highest mountain in the world?

If six children and two dogs were under an umbrella, how come none of them got wet?

Count The number of F's in the paragraph below:

"FINISHED FILES ARE THE RESULT OF YEARS OF SCIENTIFIC STUDY COMBINED WITH THE EXPERIENCE OF YEARS"