Three quarters of them are not covered.
Therefore, the island only accounts for 1/4 in the window screen, indicating that
3/4 The uncovered part accounts for 1/4 of the window.
Then when there is no cloud, the whole island will occupy (1/4)/(3/4)= 1/3.
It shows that when there are no clouds, the whole sea area should account for 1-( 1/3)=2/3.
If the white cloud occupies half of the window, it accounts for 1/4 of the island, so the island only accounts for 1/4 of the window screen.
Explain that the sea area that can be seen at that time accounts for1-(1/2)-(1/4) =1/4.
Therefore, the blocked sea area is 2/3- 1/4=5/ 12.
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