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Area of Lily at day 0=A,
Area of Lily at day 30=Area of Pond=2^30 A,

A-> 2A -> 2^2A....-> 2^30 A
takes 30days

If we start with 2 water lilies (Area at day 0 is 2A), it shall take 1 less day (29 days)

A-> 2A -> 2^2A....-> 2^30 A ­
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Bunuel
Water lily grows at such a rate that it covers double the surface that it covered the day before. It takes 30 days for a water lily to cover the entire surface of the pond. How long would it take for two water lilies of the same size to cover the entire surface of the same pond?

A. 8.33
B. 12.5
C. 15
D. 20
E. 29
Lily 1: x, 2x, 4x,.....
Lily 2: x, 2x, 4x,.....

Combining both: 2x, 4x, 8x......

In 30 days, using the formula
tn = ar^(n-1)

tn = x(2)^(29)

Formula for the situation where we have 2 lilies,
x(2)^29 = (2x)(2)^(n-1)
2^28 = 2^(n-1)

n = 29
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