What happened when the wheel was invented?

If,

20 % 5 = 24

21 % 7 = 33

42 % 6 = 67

Then;

66 % 6 = ?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

Twice ten are six of us,

Six are but three of us,

Nine are but four of us;

What can we possibly be?

Would you know more of us?

Twelve are but six of us,

Five are but four, do you see?

What are we?

What does this mean?

CCCCCCC

What does below science rebus mean?

Ag Ag Ag
Ag SPOON Ag
Ag Ag Ag

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

How can you tell a raw egg from a hard-boiled egg?

2 ladies and 2 girls need to cross a river in a boat big enough for 1 LADY or 2 girls. How do they do it?

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?