In an ap if the 12th term is13 and sum of its first four terms is 24 find the sum of its first 10 terms
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Answer:
82.1
Step-by-step explanation:
12th term = a + 11d
a + 11d = 13 - eq 1
Sum of first 4 terms = (4/2)(a + a +3d) = 24
2(2a + 3d ) = 24
2a + 3d = 12 - eq2
2*eq1 - eq2
22d - 3d = 26 - 12
19d = 14
d = 14/19
a + 11d = 13
a +11*(14/19) = 13
19a + 154 = 247
19a = 93
a = 93/19
Sum of 10 terms = (10/2)(a + a +9d)
= 5(2a +9d)
= 5 (2*93/19 + 9*14/19)
= (5/19)(186 + 126)
= (5/19)(312)
= 1560/19
= 82.1
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