1.

Find the 10th term from the end of the AP 4, 9, 14, … … … . , 254.

Answer»

Given,

AP is 4, 9, 17……...,254. 

First term of AP is a = 4. 

Common difference of AP is d = a2 – a1 

= 9 – 4 = 5. 

nth term of AP is an = 254. 

∵ an = a + (n – 1) d 

∴ a + (n – 1) d = 254 

⇒ 4 + (n − 1)5 = 254 

(a = 4 & d = 5 and an = 254) 

⇒ 5(n − 1) = 254 − 4 = 250 

⇒ n − 1 = \(\frac{250}{5}\) = 50 

⇒ n = 50 + 1 = 51.

10th term from the end of the AP is 51 – (10 – 1) = 51– 9 = 42th term of AP. 

∴ a42 = a + (42 – 1)d 

= 4 + 41 × 5 

= 4 + 205 

= 209. 

(∵a = 4,d = 5) 

Hence,

The 10th term from the end of the given AP is 209.



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