If the sum of the first 24term of an a. p is 672 and it's first term is 15. find the 20th term
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Answer:
839 / 23
Step-by-step explanation:
Sum of n terms = n /2 [ a + l ]
672 = 24 / 2 [ 15 + l ]
672 / 12 = 15 + l
l = 56 - 15
l = 24th term = 41
l = a + ( 24 - 1 ) d
41 = 15 + ( 23 ) d
26 = 23 d
d = 26 / 23
t20 = a + 19 d
= 15 + 19 ( 26 / 23 )
= 345 + 494 / 23
= 839 / 23
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