Sum of the first 14 terms of an ap is 1505 and its first term is 10 find is 25 term.
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In this question we only needed to find the common difference i.e "d" and the all we had to do was apply the formula.
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Answer: given , sn = 1505
a = 10 , n = 14
To find ; 25th term = a25
Step-by-step explanation:
sn = n/2 [ 2a + ( n - 1 )d]
1505 = 14/2 [2*10 + ( 14 - 1 ) d ]
1505 = 7 [ 20 + 13d ]
1505/7 = 20 + 13d
215 = 20 + 13d
215-20 = 13d
195 = 13d
d= 195/13
d=15
now,
a25= a + [n-1] d
a25= 10 + 24*15
a25= 10 + 360
a25= 370
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