If eleven plus two equals one, what does nine plus five equal?

Spot 5 differences in two Christmas tree below:

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

What time is it when an elephant sits on a fence?

Complete the series by replacing "?" with the correct number.

ST ND RD TH '?'

Four people need to cross a rickety bridge at night. Unfortunately, they have only one torch and the bridge is too dangerous to cross without one. The bridge is only strong enough to support two people at a time. Not all people take the same time to cross the bridge. Times for each person: 1 min, 2 mins, 7 mins and 10 mins. What is the shortest time needed for all four of them to cross the bridge?

Christina has four daughters, and each of her daughters has a brother. How many children does Christina have?

If 1+9+8=1, what is 2+8+9?

Most people think of me as money. But when they find me in the water, they won’t get any money out of me. What am I?

What is the word or phrase?