Find the missing letter in the last circle logically in the given below picture.

Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?

Do you know of a place where the wind blows south and then suddenly shifts direction towards the north?

I am weightless, but you can see me. Put me in a bucket, and I'll make it lighter. What am I?

A dying old man wants to divide his entire land between his only two sons. Since his only wish is to treat them as equal as both of them have been too good to him, he wants to divide his land equally between them. The problem is that the land is significantly irregular in shape and thus there is no choice of cutting them into two equal halves.

Can you help him divide the land in a manner that both of his sons will be happy?

In a school, there are four subjects. Seventy percent of students study English, seventy five percent of students study Science, eighty five percent of students study Mathematics and eighty percent of students study Spanish.

Can you calculate the percentage of students that study all four subjects?

A man has a barrel filled with oil that weighs 100 pounds, and then he puts something into it. Now the barrel weighs less than 100 pounds. What did he put in the barrel?

A Car is crossing a bridge 2 miles long. The bridge can only hold 10000 lbs, which is the exact weight of the car. The Car makes it half way across the bridge and stops. A bird lands on the car. Does the bridge collapse? Explain.

Take one out and scratch my head, I am now black but once was red. What am I?

I shave every day, but my beard stays the same. What am I?