19).
The probability of landing on heads the first time is 1/2.
The probability of landing on heads the second time is 1/2.
The probability of landing on heads both times is
(1/2) · (1/2) = 1/4 = 25% .
20).
The volume of the solid deck is
(length · width) · (height)
= (24 cm²) · (52 · the thickness of each car) .