Ruchi saves Rs 120 during first month ,Rs 150 in second month, Rs 180 in third month. If she continues her savings in this pattern in how many months will saves Rs 1800?
Answers
Answered by
9
Answer:
Step-by-step explanation:
Answered by
17
A.P sequence of savings = 120, 150, 180....
first term = 120 ,
common differenc = 30
sum Sn = 1800
Sn = n / 2 *[2a + (n - 1) d ]
1800 = n/ 2 * [ 2(120) + (n -1) 30]
3600 = n [240 + 30n - 30]
3600 = 240n + 30n^2 - 30n
30n^2 + 210n - 3600 = 0
30 ( n^2 + 7n - 120 ) = 0
n^2 + 7n - 120 = 0
n^2 + 15n - 8n - 120 = 0
n ( n + 15) - 8( n + 15) =0
(n + 15) ( n - 8) = 0
n = 8 , - 15
months can not count as -ve , so neglect - 15. and
take +ve value of n = 8
Answer: required months = 8 months
first term = 120 ,
common differenc = 30
sum Sn = 1800
Sn = n / 2 *[2a + (n - 1) d ]
1800 = n/ 2 * [ 2(120) + (n -1) 30]
3600 = n [240 + 30n - 30]
3600 = 240n + 30n^2 - 30n
30n^2 + 210n - 3600 = 0
30 ( n^2 + 7n - 120 ) = 0
n^2 + 7n - 120 = 0
n^2 + 15n - 8n - 120 = 0
n ( n + 15) - 8( n + 15) =0
(n + 15) ( n - 8) = 0
n = 8 , - 15
months can not count as -ve , so neglect - 15. and
take +ve value of n = 8
Answer: required months = 8 months
Similar questions