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# Differential Equation watch

1. I need help with question iii

I worked out part i and ii
the answer to i) is N=1500x2^(t/20)
the answer to ii) is N=24000

but I can't do part iii

so far I've substituted in N=3000
3000= 1500 x2^1
so t must be 20 to get 2^1

but I can't find the t value which made the population = 2000
2. (Original post by 0utdoorz)

I need help with question iii

I worked out part i and ii
the answer to i) is N=1500x2^(t/20)
the answer to ii) is N=24000

but I can't do part iii

so far I've substituted in N=3000
3000= 1500 x2^1
so t must be 20 to get 2^1

but I can't find the t value which made the population = 2000
Hint:

When N=2000

Can you do it now?

I know you're having a hard time with differential equations, but keep going at them and you'll soon be eating them for breakfast
3. (Original post by Indeterminate)
Hint:

When N=2000

Can you do it now?

I know you're having a hard time with differential equations, but keep going at them and you'll soon be eating them for breakfast
I log'd both sides
log 4/3 = (t/20) log 2
[log (4/3)/log (2) ]*20 =t
t= 8.31

Substituted that back into the equation and got 2000

then t= 20 and t=8.31

20-8.31=11.69

so it's 11 hours.....
then 0.69.... x 60 = 42 minutes

= 11 hours, 42 minutes!

thank you so much

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