Solve the Sequence Equation: Is 1 a Term in 15n - 20?

Linear Sequences with Integer Solutions

15n20 15n-20

Is the number 1 a term in the sequence above?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:06 Is number 1 part of the sequence?
00:10 Let's plug the number into the sequence formula and solve for N.
00:15 If N is a positive whole number, then it's the position in the sequence.
00:22 Now, let's isolate N in the equation.
00:34 N is positive but not a whole number. So, the number is not part of the sequence.
00:41 And that's how we solve this problem!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

15n20 15n-20

Is the number 1 a term in the sequence above?

2

Step-by-step solution

To determine if the number 1 is a term in the sequence given by 15n20 15n - 20 , we set the expression equal to 1:

15n20=1 15n - 20 = 1

Now, solve for n n :

15n20+20=1+20 15n - 20 + 20 = 1 + 20
15n=21 15n = 21

Divide both sides by 15 to solve for n n :

n=2115 n = \frac{21}{15}

Simplify the fraction:

n=75 n = \frac{7}{5}

The result, n=75 n = \frac{7}{5} , is not an integer. Since n n must be a positive integer in sequence indexing, there is no valid solution for integer n n . Therefore, the number 1 cannot be a term of this sequence.

The correct answer is No.

3

Final Answer

No.

Key Points to Remember

Essential concepts to master this topic
  • Sequence Terms: n must be a positive integer for valid terms
  • Technique: Set 15n - 20 = 1 and solve: n = 21/15 = 7/5
  • Check: Since 7/5 is not an integer, 1 cannot be a term ✓

Common Mistakes

Avoid these frequent errors
  • Accepting fractional values for n in sequences
    Don't say 'yes' just because you can solve 15n - 20 = 1 to get n = 7/5! Fractional n values don't make sense for sequence positions. Always remember that n must be a positive integer (1, 2, 3, ...) to represent actual terms in a sequence.

Practice Quiz

Test your knowledge with interactive questions

Look at the following set of numbers and determine if there is any property, if so, what is it?

\( 94,96,98,100,102,104 \)

FAQ

Everything you need to know about this question

Why can't n be a fraction in sequences?

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In sequences, n represents the position of a term (1st term, 2nd term, etc.). You can't have the 7/5th term - positions must be whole numbers!

What if I get a decimal when solving for n?

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If n comes out as a decimal or fraction, the number you're testing cannot be a term in the sequence. Only integer solutions for n produce valid sequence terms.

How do I check if any number is in this sequence?

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Set 15n20=your number 15n - 20 = \text{your number} and solve for n. If n is a positive integer, then yes! If n is negative, zero, or fractional, then no.

What numbers ARE in the sequence 15n - 20?

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Substitute positive integers: n=1 gives -5, n=2 gives 10, n=3 gives 25, etc. The sequence is -5, 10, 25, 40, 55...

Can I just plug in numbers to check?

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You could, but that's inefficient! Setting up an equation like 15n20=1 15n - 20 = 1 gives you the exact answer much faster than guessing.

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