A secret can be told only 2 persons in 5 minutes .the same person tells to 2 more persons and so on . How long will take to tell it to 768 persons ?
a)47.5 min b)50 min c) 500 min
2006-10-26 21:47:08 · 10 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
a
2006-10-26 22:02:32 · answer #1 · answered by sumone^^ 3 · 0⤊ 0⤋
This is much more complicated than it looks. Everyone else so far has gotten it wrong!
You start out with 1 person who knows a secret. They wont count in the final tally because they weren't told the secret by anybody.
After 5 minutes, that person has told 2 other people. Now 3 people know the secret, 2 have been told, so they can be added to the cumulative total, but #1 can not be. However, during the next 5 minute period all 3 will tell 2 other people the secret, making 6 new people who have learned the secret this round. That makes the cumulative total 8 and the total number of people able to tell the secret 9. so in subsequent rounds the number of tellers, tolds, and cumulative tolds will be.
min --Tellers --Tolds -Cumulate Tolds
5 -----3 -----2 -----2
10 -----7 -----6 -----8
15 ----15 ----14 ----22
20 ----31 ----30 ----52
25 ----63 ----62 ---114
30 ---127 ---126 ---240
35 ---255 ---254 --494
40 ---511 ---510 ---1004
45 --1023 --1022 --2026
50 2047 2046 4072
So after only 40 minutes there will have been more than 768 people told the secret.
2006-10-27 06:19:36 · answer #2 · answered by uselessadvice 4 · 0⤊ 0⤋
2
2 + 2*3 = 8
8+2*9 = 26
26+ 2*27 = 54
54 + 2*81 = 216
216+2*343 = 902
t = 30 min
2
2+4 = 6
6 + 12 = 18
18 + 36 = 54
54 + 108 = 162
162 + 2*162 = 486
486+2*486 = 1458
t = 35 min
to get one of your answers,
0 1
1 2
2 4
3 8
4 16
5 32
6 64
7 128
8 256
9 512
9.5 512 + 256 = 768
9.5*5 = 47.5
2006-10-27 05:26:37 · answer #3 · answered by Helmut 7 · 0⤊ 1⤋
A quiker way is to say that 1+summation of 2^i from i=1 up till x is equal to 768 and solve for x. Using the rules regarding summation formulas.
once you have x you multiply it by 5.
x=9.5
x*5=47.5
2006-10-27 06:08:33 · answer #4 · answered by Faz 4 · 0⤊ 0⤋
50 mins: 2 x itself 10 times is 1024, so 10 times 5 mins is 50
2006-10-27 05:06:29 · answer #5 · answered by Anonymous · 0⤊ 0⤋
The amazing thing is how many people say 47.5 minutes. Why does math preclude common sense so often?
2006-10-27 08:26:07 · answer #6 · answered by Nomadd 7 · 0⤊ 0⤋
384
2006-10-29 01:01:14 · answer #7 · answered by CHEROKEEMAN2 2 · 0⤊ 0⤋
its more complicating......I'm sure 307.2 coz
768 / 5=153.6
153.6 x 2= 307.2mins............am i ryt?
2006-10-27 04:56:45 · answer #8 · answered by Raji 5 · 0⤊ 0⤋
my ans is 47.5min
2006-10-27 04:57:00 · answer #9 · answered by samdesign78 6 · 0⤊ 0⤋
its got to be (a)
2006-10-27 04:58:34 · answer #10 · answered by Yvonne Mystic 4 · 0⤊ 0⤋