Math Problem Statement

888-880+872-864+856-848+...+24-16+8

Solution

To solve the expression 888880+872864+856848++2416+8888 - 880 + 872 - 864 + 856 - 848 + \dots + 24 - 16 + 8, we first recognize a pattern in the sequence.

This sequence alternates between addition and subtraction of terms that decrease by 8 each time. We can group each pair of terms together:

(888880)+(872864)+(856848)++(2416)+8(888 - 880) + (872 - 864) + (856 - 848) + \dots + (24 - 16) + 8

Each pair simplifies as follows:

888880=8,872864=8,856848=8,888 - 880 = 8, \quad 872 - 864 = 8, \quad 856 - 848 = 8, \quad \dots

So each pair contributes 88 to the total sum.

Next, we count the number of pairs in the sequence. The sequence starts at 888 and decreases by 8 until it reaches 16 (or 24 when the last term is single). This sequence can be described by:

888,872,856,,24888, 872, 856, \dots, 24

To find the number of terms in this arithmetic sequence:

  1. First term a1=888a_1 = 888.
  2. Last term an=24a_n = 24.
  3. Common difference d=16d = -16.

The number of terms nn in the sequence is given by:

an=a1+(n1)da_n = a_1 + (n-1) \cdot d

Plugging in the values:

24=888+(n1)(16)24 = 888 + (n-1)(-16)

24888=(n1)(16)24 - 888 = (n-1)(-16)

864=(n1)(16)-864 = (n-1)(-16)

n1=86416=54n-1 = \frac{864}{16} = 54

n=55n = 55

Since each pair contributes 8, the sum is:

Number of pairs×8=552×8=27.5×8=220\text{Number of pairs} \times 8 = \frac{55}{2} \times 8 = 27.5 \times 8 = 220

So, the total sum is 220.

Would you like any further details on this process or have any questions?


Here are some related questions to deepen your understanding:

  1. How would the sum change if the sequence started at a different number?
  2. What happens if the sequence alternated between addition and subtraction but had a different common difference?
  3. How would you handle a sequence where the pattern isn't immediately obvious?
  4. Can you find the sum of a similar sequence that increases instead of decreases?
  5. What if the sequence ended in a negative number? How would that affect the sum?

Tip: When dealing with sequences, always look for patterns and try grouping terms to simplify the problem.

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Math Problem Analysis

Mathematical Concepts

Arithmetic Sequences
Summation of Series

Formulas

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Theorems

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Suitable Grade Level

Grades 9-12