Answer:
a. 675
b. 3
Explanation:
a.
The number of consecutive numbers is ...
N = L -F +1 = 38 -12 +1 = 27
Then the forumula tells you the sum of numbers from 12 to 38 is ...
S = N/2(F +L) = 27/2(12 +38) = (27)(50)/2 = 575
The sum of the 27 consecutive numbers from 12 to 38 is 575.
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b.
Solving the above formula for N so that it has F as the object, we get ...
F = L +1 -N
Then the first number of 15 consecutive numbers ending in 17 is ...
F = 17+1 -15 = 3
The first number is 3.
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The sum of the numbers is S = (15/2)(3 +17) = 150, as given. This information is redundant (not needed in the solution process).