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.
The quantities in the proportion you give add to 16 pounds, of which 2 pounds are cement. That is, cement constitutes 1/8 of the total weight.
For each yard of concrete, 4000 lb/8 = 500 lb of cement are used.
For 12.5 yards of concrete, 12.5 * 500 = 6,250 pounds of cement will be used.
_____
"yard" in this case is shorthand for "cubic yard".
Answer:
Wetlands prevent flooding by temporarily storing and slowly releasing stormwater.
Step-by-step explanation:
Wetlands also reduce water flow, thus allowing sediments and associated pollutants to settle out. A marshland can prevent flooding in a nearby town bye temporarily storing water!
1/7 is bigger because a negative number is always smaller than a positive number no matter how big
