Answer:
see explanation
Step-by-step explanation:
the sum to n terms of an arithmetic sequence is
=
[2a + (n - 1)d ]
where d is the common difference and a is the first term
here d = 9 - 7 = 7 - 5 = 2 and a = 5, hence
=
[(2 × 5) + 2(n - 1) ]
=
(10 + 2n - 2)
=
(2n + 8)
= n² + 4n
When sum = 165, then
n² + 4n = 165 ← rearrange into standard form
n² + 4n - 165 = 0 ← in standard form
(n + 15)(n - 11) = 0 ← in factored form
equate each factor to zero and solve for n
n + 15 = 0 ⇒ n = - 15
n - 11 = 0 ⇒ n = 11
but n > 0 ⇒ n = 11
Answer:
Each pencil cost $0.51
Step-by-step explanation:
Answer:
95k
Step-by-step explanation:
Given :
15 words or less = 50k
Every word above 15 = additional 3k
The cost of 30 words :
First 15 words = 50 k
Number of additional words = (30 - 15) = 15 words
Cost of every additional word = 3 k
Cost of 15 additional word = 15 * 3 = 45k
Total cost of 30 words :
50k + 45k = 95k