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 = 
The building is 231.7 m far away.Distance can refer to a physical length or an estimate based on other factors in physics or common use.
<h3>What is distance?</h3>
Distance is a numerical representation of the space between two objects or locations. |AB| is a symbol for the distance between two points A and B.
Given data;
Speed of sound = 331 meters per second
Time = 0.7 sec
The distance from the building is;
d=v×t
d=331 m/sec × 0.7 sec
d=231.7 m
Hence the building is 231.7 m far away.
To learn more about the distance refer to the link;
brainly.com/question/26711747
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305 divided by 12.2 equals 25. Have a nice day! ^ U ^
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