Why do we preferably have round manhole covers and not square ones?

Make a sentence consisting of three words that have the whole alphabet.

Consider this about a word: The first two letters signify a male, the first three letters signify a female, the first four letters signify a great, while the entire world signifies a great woman. What is the word?

In the image given, you can find several triangles. Can you count them all?

Find The Next Number in the series:

12 13 15 17 111 113 117 119 123 ?

A sundial has the fewest moving parts of any timepiece. Which has the most?

John is the son of Jacob.
So,
Jacob is the_____of John's father?

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.

What is so fragile that saying its name breaks it?

Can you divide numbers from 1 to 9 (1 2 3 4 5 6 7 8 9) into two groups so that the sum of the numbers of each group is equal?

Note: 9 cannot be turned over to make it 6.