bb wrote:
Adding one more for today:
If you are doing well and heading for 700+ score, you can always expect a questions you won't know how to solve. Try this one for example.
A fast-growing water lily doubles in size every day and it takes 30 days for a water lily to cover the entire surface of the pond. How many days would it take for the water lilly to cover half the pond?
A. 8.33
B. 12.5
C. 15
D. 20
E. 29
Well, that's an interesting as well as a tricky question. At first I was also falling into trap, if I am getting it right this time.
Suppose, if I plant water lily of \(1 cm\) today then it will be doubled today to \(2 cm\) and then after tomorrow it will become \(4 cm\) after doubling again.
Days: \(1, 2, 3, 4, 5,....., 30\)
Size: \(2, 4, 8, 16, 32,.....,30th value\) ---> 30th value on 30th day.
Size: \(2^1, 2^2, 2^3, 2^4, 2^5, .....,2^ 30\)
We conclude that in 30 days its size will be \(2^30\) cm which will cover the whole pond and we can say that size of pond is \(2^ 30 cm\).
Size of half pond will be --> \(\frac{2^ 30}{2}cm = 2^ 29 cm\) --->29th value will be on 29th day. It will take
29 days for water lily to cover half of the pond.
Hence, answer should be
E.
I could easily go for
15 days by falling into the trap but soon I realised that it is doubling every day which means twice of the size of the every previous day.
Let me know if I am right or not. And, how can I make the exponent 30 of any base value together here on GClub as 3 & 0 appear separately in the power?