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If the Common Differences of an A.P. is 3, Then A20 − A15 is - Mathematics

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ConceptSum of First n Terms of an AP

Question

If the common differences of an A.P. is 3, then a20 − a15 is 

  • A. 5

  • B. 3

  • C. 15

  • D. 20

Solution

Let the first term of the A.P. be a

`a_n=a(n-1)d`

`a_20-a_15=[a+(20-1)d]-[a+(15-1)d]`

`=19d-14b`

`=5d`

`=5xx3`

`=15`

The correct answer is C. 

  Is there an error in this question or solution?
Solution If the Common Differences of an A.P. is 3, Then A20 − A15 is Concept: Sum of First n Terms of an AP.
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