Question:

The number of terms common to two A.P.'s $3, 7, 11,..........., 407$ and $ 2, 9, 16,............,709$ is

Updated On: Feb 9, 2025
  • 14
  • 21
  • 28
  • none of these
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The Correct Option is A

Solution and Explanation

By inspection. First common term to both the series is $23$. Second common term $= 51 $ Third $= 79$ and so on. These nos. form an $A.P . 23,51,79 ..... $ Since $T_{15} = 23 + 14 (28) $ $= 23 + 392 = 415 > 407 $ and $T_{14} = 23 + 13 (28) = 387 < 407$. $\therefore$ number of common terms $= 14$.
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Concepts Used:

Arithmetic Progression

Arithmetic Progression (AP) is a mathematical series in which the difference between any two subsequent numbers is a fixed value.

For example, the natural number sequence 1, 2, 3, 4, 5, 6,... is an AP because the difference between two consecutive terms (say 1 and 2) is equal to one (2 -1). Even when dealing with odd and even numbers, the common difference between two consecutive words will be equal to 2.

In simpler words, an arithmetic progression is a collection of integers where each term is resulted by adding a fixed number to the preceding term apart from the first term.

For eg:- 4,6,8,10,12,14,16

We can notice Arithmetic Progression in our day-to-day lives too, for eg:- the number of days in a week, stacking chairs, etc.

Read More: Sum of First N Terms of an AP