size = a(2)^t , where t is the number of days
when t = 30 , size = 6
6 = a(2)^30
a = 6/2^30
1.5 = ( 6/(2^30) )( 2^t)
1.5 = 6 (2^(t-30) )
.25 = 2^(t-30)
log .25 = log 2^(t-30)
log .25 = (t-30)log 2
log .25/log 2 = t-30
t = log .25/log 2 + 30 = appr 23.356
23 days and 8.5 hours
A fast growing mushroom doubled in size every day. After 30 days, it measured 6 inches tall. On which day did it measure 1 1/2 inches tall?
2 answers
Hmmm. It doubles every day.
6 = 4 * 1 1/2, so it must have taken the last 2 days to double twice from 1 1/2 to 3 to 6 inches.
I say it took 28 days.
I'd have stopped at
.25 = 2^(t-30)
-2 = t-30
t = 28
Not sure what went wrong after that.
6 = 4 * 1 1/2, so it must have taken the last 2 days to double twice from 1 1/2 to 3 to 6 inches.
I say it took 28 days.
I'd have stopped at
.25 = 2^(t-30)
-2 = t-30
t = 28
Not sure what went wrong after that.
2 answers