1 What is the sum of the first 20 terms of this sequence (5, 15, 25,...)?
2.What is the sum of the first 15 terms of this sequence (5, 9, 13,)?
3.In an arithmetic series, find the sum of the first 20 terms if the first term is -12 and the common difference is -5.
4.Find the sum of the series 14+11+8+...+ -82
5. How many terms of the arithmetic 2 3. 4. 6. A PROBLEM 7. sequence (1,3,5,7,) will give a sum of 961?
6.In an arithmetic series, a = -14 and as= 30. Find the sum of the first 20 terms.
7.How many terms of the arithmetic sequence (2,4,6,8,) will give a sum of 600?
2.What is the sum of the first 15 terms of this sequence (5, 9, 13,)?
3.In an arithmetic series, find the sum of the first 20 terms if the first term is -12 and the common difference is -5.
4.Find the sum of the series 14+11+8+...+ -82
5. How many terms of the arithmetic 2 3. 4. 6. A PROBLEM 7. sequence (1,3,5,7,) will give a sum of 961?
6.In an arithmetic series, a = -14 and as= 30. Find the sum of the first 20 terms.
7.How many terms of the arithmetic sequence (2,4,6,8,) will give a sum of 600?
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Answer:
1. S20= 20/2[2(5)+(20-1)10]
=10(10+190)
=10(200)
=2000
The 20th term of the sequence is 195, so the sum is 2000
2a1=5 n=15 d=4 s15=?
=15/2(2(5)+(15-1)4)
=7.5(10+(14)4)
=7.5(10+56)
=7.5(66)
=495
3.Correct option is A)
First term =a=−12
n=20
d=−5
S
n
=
2
n
[2a+(n−1)d]
S
20
=
2
20
[2×−12+(20−1)(−5)]
S
20
=10[−24−95]
S
20
=−1190