Check the picture below.
now, keep in mind that ship B is going at 20kph, thus from noon to 4pm, is 4 hours, so it has travelled by then 20 * 4 or 80 kilometers, thus b = 80.
whilst the ship B is moving north, the distance "a" is not really changing, and thus is a constant, that matters because the derivative of a constant is 0.
 
 
        
        
        
Answer:

Step-by-step explanation:
We are given the two functions: 

And we want to find: 

So, by substitution: 

Simplify. Distribute: 

Rearrange: 

Combine like terms. Hence: 

 
        
             
        
        
        
Answer:
1,2 and 4 are equivalents. 3 is not equivalent
2P-I, mark that one :l
Step-by-step explanation:
 
        
             
        
        
        
Answer:
(1 ) Inner curved surface area of the well is  109.9 sq. meters.
(2) The cost of plastering the total curved surface area is  4396.
Step-by-step explanation:
The inner diameter = 3.5 m 
Depth of the well =  10 m
Now, Diameter = 2 x Radius
⇒R = D/ 2  = 3.5/2 = 1.75
or, the inner radius of the well = 1.75 m
CURVED SURFACE AREA of cylinder = 2πr h
⇒The inner curved surface area =  2πr h  = 2 ( 3.14) (1.75)(10)
                                                                       = 109 sq. meters
Hence, the inner curved surface area of the well is  109.9 sq. meters.
Now, the cost of plastering the curved area is 40 per sq meters
So, the cost of total plastering total area = 109.9 x(Cost per meter sq.)
                                                                     =  109.9 x (40)
                                                                    =   4396
Hence, the cost of plastering the total curved surface area is  4396.
 
        
             
        
        
        
Answer:
18 1/2 or 37/2
Step-by-step explanation:
To calculate the average of something, we add the numbers and divide by the count of those numbers. In this case, we have this as the sum of the numbers:
9 × 20 + 4 × 19 + 3 × 18 + 5 × 17 + 12
And the number of students as the count:
9 + 4 + 3 + 5 + 1
Now to calculate that out: 
(9 × 20 + 4 × 19 + 3 × 18 + 5 × 17 + 12)/(9 + 4 + 3 + 5 + 1) ⇒
(180+76+54+85+12)/(9+4+3+5+1) ⇒
407/22 ⇒
37/2⇒
18 1/2