Question

if 1 hen lays 1 egg in 1 day, how many eggs 2 hens lay in 2 days?

Answer 1

Such a question causes often confusion  by quick thinking.. and hurry.  Some people could quickly say 2.  But answer is some thing else.

Answer is two eggs are laid by each hen in two days.

   So a total of four eggs are laid by the two hen in two days.

Answer 2

let ther be 2 hen 
 x 
and 
y 
x will lay 1 egg in one day. so 2  egg in 2 days
 y will lay 1 egg in one days  2 egg in 2 days

therefore

2+2 =4