Math Problem Statement

Find the sum from n=1 to n=60 of (3n - 9).

Solution

The given problem asks to find the sum:

n=160(3n9)\sum_{n=1}^{60} (3n - 9)

We can break this sum down and solve it step by step.

Step 1: Break the summation into two parts.

n=160(3n9)=n=1603nn=1609\sum_{n=1}^{60} (3n - 9) = \sum_{n=1}^{60} 3n - \sum_{n=1}^{60} 9

This separates into two simpler sums: one involving 3n3n and the other a constant 99.

Step 2: Calculate the first summation: n=1603n\sum_{n=1}^{60} 3n

The constant 33 can be factored out: 3n=160n=360(60+1)2=360×612=31830=54903 \sum_{n=1}^{60} n = 3 \cdot \frac{60(60 + 1)}{2} = 3 \cdot \frac{60 \times 61}{2} = 3 \cdot 1830 = 5490

Step 3: Calculate the second summation: n=1609\sum_{n=1}^{60} 9

Since 99 is constant, this is simply: 9×60=5409 \times 60 = 540

Step 4: Subtract the two results:

5490540=49505490 - 540 = 4950

Thus, the sum is:

4950\boxed{4950}

Would you like more details or have any questions?

Here are 5 related questions:

  1. How would the sum change if the upper limit of the summation were n=100n = 100?
  2. How can you use properties of arithmetic progressions to solve similar summation problems?
  3. What is the general formula for the sum of the first nn natural numbers?
  4. How would you sum an expression with quadratic terms, such as (n25n)\sum (n^2 - 5n)?
  5. How does factoring constants out of summations simplify the process?

Tip: Always look for ways to split and simplify summation problems by separating constants and variable-dependent terms.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Algebra
Summation
Arithmetic Sequences

Formulas

Sum of first n natural numbers: S = n(n+1)/2
Sum of constants: S = constant * n

Theorems

Arithmetic progression sum

Suitable Grade Level

Grades 9-12