21.
When was the first lawn mower invented?

22.
In which decade were the first successful diode and triode vacuum tubes invented?

23.
Who is the English physicist responsible for the 'Big Bang Theory'?

24.
What 'game' was first produced by the Southern Novelty Company in Baltimore, Maryland in 1892?

25.
Which insurance salesman invented the fountain pen in 1884?

26.
When was the first elevator built?

27.
What charge card, developed in 1950, was the first to be accepted nationally in the US?

28.
What Enrico Fermi invented?

29.
Which of the following was first patented by an Australian in 1889?

30.
Who among the following invented the small pox vaccine?