Answer:
12-10=2
2 parts of 10 is 20 percent.
The rate went up 20%.
let
x---------> Aviva’s age
y--------->Kanti’s age
z--------> Lakshmi’s age
we know that
y=x-3-----> equation 1
z=2*y-----> equation 2
substitute equation 1 in equation 2
z=2*(x-3)
so
Aviva’s age------> x
Kanti’s age-------> x-3
Lakshmi’s age----> 2*(x-3)
therefore
the answer is the option
b) 2(x-3)
This question is the application of differential eqns in order to derive a model for the temperature dependence with time. Actually, a general equation has already been derived for this type of cases. This equation is known as the Newton's Law of Cooling. The equation is
(T - Ts) / (To -Ts) = e^(-kt)
where T is the the temperature at any time t
Ts is the surrounding temperature
To is the initial temperature
k is the constant
t is the time
several assumptions have been made to arrive at this form, i suggest you trace the derivation of the general formula.
First we need to look for k using the initial conditions that is @t = 1.5 min, T = 50 F
substituting we get a k = 0.2703
therefore @ t = 1 min, T = 55.79 F
@ T = 15 F the time required is 9.193 min.
