a) 285
b) 350
c) 325
d) 365
The given series has six terms. What is the sum of the terms of the series? 10 + 25 + 40 + . . . + 85?
2016-06-30 10:57 am
回答 (2)
2016-06-30 11:04 am
10 + 25 + 40 + . . . + 85
This is the sum an arithmetic sequence.
The first term, a₁ = 10
The last term, an = 85
The Common difference, d = 25 - 10 = 40 -25 =15
an = a₁ + (n - 1)d
85 = 10 + (n - 1) × 15
(n - 1) × 15 = 75
n - 1 = 5
n = 6
Sum, S(6)
= n (a₁ + an) / 2
= 6 × (10 + 85) / 2
= 285
...... The answer is a) 285
This is the sum an arithmetic sequence.
The first term, a₁ = 10
The last term, an = 85
The Common difference, d = 25 - 10 = 40 -25 =15
an = a₁ + (n - 1)d
85 = 10 + (n - 1) × 15
(n - 1) × 15 = 75
n - 1 = 5
n = 6
Sum, S(6)
= n (a₁ + an) / 2
= 6 × (10 + 85) / 2
= 285
...... The answer is a) 285
2016-06-30 11:07 am
A) 285.
10 + 25 + 40 + 55 + 70 + 85 = 285
10 + 25 + 40 + 55 + 70 + 85 = 285
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