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Find A30 − A20 For the A.P. −9, −14, −19, −24, ... - Mathematics

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प्रश्न

Find a30 − a20 for the A.P.

−9, −14, −19, −24, ...

उत्तर

In this problem, we are given different A.P. and we need to find `a_30 - a_20`.

A.P. −9, −14, −19, −24, ...

Here

First term (a) = -9

Common difference of the A.P. (d) = - 14 - (-9)

= -14 + 9

= -5

Now as we know

`a_n = a + (n -1)d`

Here we find `a_30` and `a_20`

So for 30 th term

`a_30 = a + (20 - 1)d`

`= -9 + (19)(-5)`

= -9 - 95

= -104

So

`a_30 - a_20 = -154 - (-104)`

=-154 + 104

= -50

Therefore for the given A.P `a_30 - a_20 = -50`

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अध्याय 5: Arithmetic Progression - Exercise 5.4 [पृष्ठ २५]

APPEARS IN

आरडी शर्मा Mathematics [English] Class 10
अध्याय 5 Arithmetic Progression
Exercise 5.4 | Q 20.1 | पृष्ठ २५

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Case Study

Push-ups are a fast and effective exercise for building strength. These are helpful in almost all sports including athletics. While the push-up primarily targets the muscles of the chest, arms, and shoulders, support required from other muscles helps in toning up the whole body.


Nitesh wants to participate in the push-up challenge. He can currently make 3000 push-ups in one hour. But he wants to achieve a target of 3900 push-ups in 1 hour for which he practices regularly. With each day of practice, he is able to make 5 more push-ups in one hour as compared to the previous day. If on first day of practice he makes 3000 push-ups and continues to practice regularly till his target is achieved. Keeping the above situation in mind answer the following questions:

  1. Form an A.P representing the number of push-ups per day and hence find the minimum number of days he needs to practice before the day his goal is accomplished?
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