Solve for the 11th Term in Sequence: 2, 5, 8, ...

Arithmetic Sequences with Term Calculation

Assuming the sequence continues according to the same rule, what number appears in the 11th element?

2,5,8 2,5,8\ldots

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find the 11th term
00:03 This is the sequence formula
00:07 Let's substitute the appropriate term position in the formula and solve
00:13 Always solve multiplication and division before addition and subtraction
00:16 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Assuming the sequence continues according to the same rule, what number appears in the 11th element?

2,5,8 2,5,8\ldots

2

Step-by-step solution

To solve this problem, we'll follow these steps:

  • Step 1: Identify the rule of the sequence
  • Step 2: Use the rule to find the 11th term

Now, let's work through each step:
Step 1: The given sequence starts with 2, 5, 8. We determine the pattern by finding the difference between consecutive terms:
52=3 5 - 2 = 3 and 85=3 8 - 5 = 3 so the common difference (d d ) is 3.
This indicates it is an arithmetic sequence with a1=2 a_1 = 2 and d=3 d = 3 .

Step 2: Use the arithmetic sequence formula to find the 11th term a11 a_{11} :
an=a1+(n1)d a_n = a_1 + (n-1)d
Substitute the known values:\
a11=2+(111)3 a_{11} = 2 + (11-1) \cdot 3
a11=2+103 a_{11} = 2 + 10 \cdot 3
a11=2+30 a_{11} = 2 + 30
a11=32 a_{11} = 32

Therefore, the 11th element in the sequence is 32 32 , which corresponds to choice 32 32 .

3

Final Answer

32

Key Points to Remember

Essential concepts to master this topic
  • Pattern Recognition: Find common difference by subtracting consecutive terms
  • Formula Application: Use an=a1+(n1)d a_n = a_1 + (n-1)d where d=3, n=11
  • Verification: Check by counting: 2+3=5, 5+3=8, continuing to 11th term ✓

Common Mistakes

Avoid these frequent errors
  • Confusing position number with term value
    Don't think the 11th term equals 11 = wrong answer! Students mix up the position (11th) with the actual value (32). Always use the arithmetic sequence formula to find the term value, not just the position number.

Practice Quiz

Test your knowledge with interactive questions

12 ☐ 10 ☐ 8 7 6 5 4 3 2 1

Which numbers are missing from the sequence so that the sequence has a term-to-term rule?

FAQ

Everything you need to know about this question

How do I know this is an arithmetic sequence?

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Check if the difference between consecutive terms is constant. Here: 5-2=3 and 8-5=3. Since the difference is always 3, it's arithmetic!

What if I can't remember the formula?

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You can count up by the common difference! Start with 2, then add 3 ten more times: 2, 5, 8, 11, 14, 17, 20, 23, 26, 29, 32. The formula is just faster!

Why do we use (n-1) instead of just n?

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Because we start counting from the first term! To get from the 1st to the 11th term, we only add the common difference 10 times (11-1=10), not 11 times.

Can I work backwards to check my answer?

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Absolutely! If the 11th term is 32, then the 10th term should be 32-3=29, the 9th term should be 29-3=26, and so on. This confirms your answer!

What if the sequence had a different starting number?

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The method stays the same! Just use the new first term as a1 a_1 in the formula. For example, if it started with 5, then a1=5 a_1 = 5 instead of 2.

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