Answer:
Step-by-step explanation:
1:9:3
brian gets x
alex gets 9x
colin gets 3x
Brian and colin receive 40
x + 3x = 40
x = 10
alex gets 9x = £90
Answer:
4712.4
Step-by-step explanation:
I got the same question a few days ago.
The volume is πr^2 * h / 3
r = 15
h = 20
225π * 20 / 3
1500π
It's 4712.38898
Round to 4712.4
Answer:
a)
, b)
, c)
, d) 
Step-by-step explanation:
a) Let assume an initial mass m decaying at a constant rate k throughout time, the differential equation is:

b) The general solution is found after separating variables and integrating each sides:

Where
is the time constant and 
c) The time constant is:


The particular solution of the differential equation is:

d) The amount of radium after 300 years is:

A = 4πr² Divide both sides by 4π
A / 4π = r² Find the square root of both sides
√(A / 4π) = √(r²) Cancel out the square with the square root
√(A / 4π) = r Switch the sides to make it easier to read
r = √(A / 4π)