In mathematical notation, ∑ means summation. So wherever you see the symbol, you have to sum over all elements in the set. Let's solve the question.
a. ∑m means, to sum all elements in the set m: ∑m = 12 + 15 + 20 + 30 = 77
b. ∑
means to sum all elements in the set f as the square of the elements f = 
c. ∑mf means to sum all elements as the product of the elements of m and f = (12×5) + (15×9) + (20
10) + (30×16) = 875
d. ∑
means to sum all elements as the product of the square of m and f = 
Answer:
240 m
Step-by-step explanation:
Figure is attached.
The distance the particle travels is the area under the v-t graph over the time interval from 0 min to 4 min. The reason you can't just multiply velocity by time is that the velocity is changing at a constant rate over the given time interval (the line is going upward--the particls is speeding up).
What's the area under the graph?
The red outline forms a trapezoid. The area of a trapezoid is
where the <em>b</em>'s are the lengths of the two parallel base and <em>h</em> is the height (the distance between the bases).
Reading the graph carefully (notice the scales!)...

Answer:
dh/dt = 3/25π m/min
Step-by-step explanation:
Radius = 5m
Rate (dV/dt) = 3 cm^3 / min
Leaking rate = 1 cm^3 / min
Volume = πr^2h
Volume = π(5)^2h
V= 25πh
Differentiate volume implicitly with respect to time
dV/dt = 3 cm^3/min
3 = 25π(dh/dt)
dh/dt = 3 m^3/min /25πm^2
dh/dt = 3/25πm/min