When can we add 2 to 11 and get 1 as the correct answer?

There are three Athletes (John, Tarun and Harish) and their individual Coaches (Jacob, Meenaxi and Priyanka) standing on the shore.
No Coach trusts their Athlete to be near any other Coach unless they are also with them.
There is a boat that can hold a maximum of two persons.
How can the six people get across the river?

At a party, there are five people and a whole round cake lying at the centre of the table. Only four people will make a cut and take their piece and the last one will get the remaining piece on the table. How can they make sure that everyone gets a 1/5th of the piece?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?

What is the next number in this matchsticks series riddle?

What two things can you never eat for breakfast?

Pronounced as one letter,
And written with three,
Two letters there are,
And two only in me.
I am double, I am single,
I am black blue and grey,
I am read from both ends,
And the same either way.

I can write cow in 13 letters.

Can You?

What has to be broken before you can use it?

Prove that the below maths equation is true.

8 + 8 = 91