CPM Homework Help : PC Problem 7-95

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Home > PC > Chapter 7 > Lesson 7.3.1 > Problem 7-95

7-95.

Find the following sums.

$3 + 6 + 9 + … + 90$
Steps (a):
Add the first and last terms.
Divide by 2.
Multiply by the number of terms.
Answer (a):
$\frac{30(3+90)}{2}=1395$

$20 + 22 + 24 + … + 100$
Hint (b):
How many terms are there?
Hint Answer (b):
$41$

$\displaystyle \sum _ { n = 1 } ^ { 41 } 2 n + 18$
Steps (c):
Add the first and last terms.
Divide by 2.
Multiply by the number of terms.

$\displaystyle \sum _{ k = 8 } ^ { 53 } 5 k - 3$
Hint (d):
How many terms are there? That is, if the sum started with k = 1, what would it end with?
Hint Answer (d):
$46$

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