2 Answers

Tom Stambaugh · Answer 1 · 2020-11-09T22:31:40+0000

The plate consists of 70 (7*10) squares with dimensions 1x1 square mm. Let
be the number of white squares and
the number of black squares. Then

b+w=70

We're told there are 2 more black squares than white, so

b=2+w

Then

$(2+w)+w=2+2w=70\implies1+w=35\implies w=34$

so there are 34 white squares and 36 black squares. The probability that Crystal is looking at a white square is

(34)/(70)=(17)/(35)

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