7) E

P (first one being red) = 3/6 = 1/2
P (second one being yellow) = 3/5
P (third one being red) = 2/4 = 1/2
P (fourth one being yellow) = 2/3
P (fifth one being red) = 1/2
P (sixth one being yellow) = 1/1

1/2 x 3/5 x 1/2 x 2/3 x 1/2 x 1/1 =  6 /120 = 1/20

There are two situations which can satisfy our need:

R – Y – R – Y – R – Y
Y – R – Y – R – Y – R

Since there are two situations we need to multiply the probability we obtained by 2.
So probability of having alternate coloured flowers = 2 x 1/20 = 2/20 = 1/10

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