If a field is 900 meters squared and one side is twice as big as the other how big is each side
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 = 
Because she had the $12 dollars on their but she can only use it at a certain store
To solve, you first want to find the total she hiked in the morning. 1.75+2.4=4.15. Then, you want to subtact the total miles she hiked in the morning from the total miles she hiked in total. 6.5-4.15=2.35. The last step is to compare the miles hiked in the morning compared to the miles in the afternoon by finding the difference. 4.15-2.35=1.8, so therefore she hiked 1.8 more miles in the morning than in the afternoon,