If you toss a coin 10 times and it lands heads up every time, what are the chances it will land heads up if you toss it again?

Can you find a pattern and the missing number in the series given below?

100, 155, 258,? , 584, 819.

Speaking of rivers, a man calls his dog from the opposite side of the river. The dog crosses the river without getting wet, and without using a bridge or boat. How?

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

Two boys were admitted to a school. When the headmaster asks them about their parents, they tell him that they have same parents (father and mother). On further inquiry, it turns out that they both share the same date for their birthday.

"Are you twins," ask the headmaster.
"No," replies the boys.

Is it possible?

The more you take me, the more you leave me behind.
Who Am I?

Considering the below equation:

V + II - VI = 10
IV - X + VIII = 20
IV - VII + VI = 30

Then, I + II + III = ?

Suppose you are a girl candidate and sitting in an interview. Suddenly the interviewer asks you, 'What if one morning you wake up and find out that you are pregnant?

How will you reply to such a question?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?

If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?