What four weights can be used to balance from 1 to 30 pounds?

Find The Next Number in this series.
1, 2, 6, 42, 1806 ?

Count the number of triangles in the below picture?

What's a single-digit number with no value?

Find a 9-digit number, which you will gradually round off starting with units, then tenth, hundred etc., until you get to the last numeral, which you do not round off. The rounding alternates (up, down, up ...). After rounding off 8 times, the final number is 500000000. The original number is commensurable by 6 and 7, all the numbers from 1 to 9 are used, and after rounding four times the sum of the not rounded numerals equals 24.

Be active and find the killer in the picture Riddle below.

What is the relationship between these matchstick pictures below?

He does not have any heart but still, He manages to live.
If you kill him, you will eventually die but yet you kill him.
He cannot run, who is He?

An exterior architect is asked by a builder to plant seven trees in a manner that there are exactly six rows of trees in a straight line and each row has three trees in particular.

How will he do it?

Cristina was born in 1888. She just had her 30th birthday today how did that happen?