Respuesta :
Sum of AP =
(n/2) (2a + (n - 1)d)
You have a = 10, d = 3, and want to know how long to reach a total of 900.
(n/2) (20 + (n - 1) 3) < 900
n(20 + 3n - 3) < 1800
3n² - 17n < 1800
Use the quadratic equation to solve
3n² - 17n - 1800 = 0, which gives
n = 21.8
so to get less than 0 on the right-hand side, 21 is the nearest integer.
Thus, in 21 weeks, she saves a total of
(21/2) (2*10 + (20)3)
= (21/2) (80) = 840
which leaves her 60 to save in week 22.
https://answers.yahoo.com/question/index?qid=20140506142856AArhap0&guccounter=1
The saving for the final week will be equal to $60.
What is an arithmetic progression?
The sequence in which every next number is the addition of the constant quantity in the series is termed the arithmetic progression.
Sum of AP =(n/2) (2a + (n - 1)d)
It is given that Dreya is saving money to purchase a $900 computer, and she saves $10 in the first week. Each week after that, she saves $3 more than the previous week, except in the last week, when she reaches $900.
The saving for the last week will be calculated as:-
Given that a = 10, d = 3,
(n/2) (20 + (n - 1) 3) < 900
n(20 + 3n - 3) < 1800
3n² - 17n < 1800
Use the quadratic equation to solve further.
3n² - 17n - 1800 = 0, which gives
n = 21.8
To get less than 0 on the right-hand side, 21 is the nearest integer.
Thus, in 21 weeks, she saves a total of,
Saving for 21st week =(21/2) (2 x 10 + (20)3)
Saving for 21st week= (21/2) (80) = 840
Therefore, the saving for the final week will be equal to $60.
To know more about arithmetic progression follow
https://brainly.com/question/6561461
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