What is the centre of gravity?

A research team went to a village somewhere between the jungles of Africa. Luckily for them, they reached the day when quite an interesting custom was to be performed. The custom was performed once a year as they confirmed and was performed in order to collect the taxes from every male of the region.

The taxes were to be paid in the form of grains. Everyone must pay pounds of grain equaling his respective age. This means a 20-year-old will have to pay 20 pounds of grain and a 30-year-old will pay 30 pounds of grain and so on.

The chief who collects the tax has 7 weights and a large 2-pan scale to weigh. But there is another custom that the chief can weigh only three of the seven weights.

Can you find out the weights of the seven weights? Also, what is the maximum age of the man that can be weighed for the payment of taxes?

Is the statement valid that it does not matter how much older a sibling is, eventually the younger one will be half as old as the older one?

Decode below three cipher riddles:

26 L of the A
7 D of the W
1000 Y in a M

What do you think with the below Picture ?

I went to the bookshop and spent one-half of the money that was in my purse.

When I came out, I found that I had as many cents as I had dollars and half as many dollars as I had cents when I went in. Find the money in my purse when I entered the store.

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

ENEMY = 2 * LINK
LINK + 2 = HELL

Then what will be TAXI + HELL? Select from the options below:
a) ROTTEN
b) DANGER
c) HEAVEN
4) MORTAL

There are a number of books on a shelf. If one book is the 4th from the left and 6th from the right, how many books are on the shelf?

How much will a 38° angle measure when looked at under a microscope that magnifies ten times?