Sn=3250
a=305
d=-15
formula:Sn=n/2[2a+(n-1)d]
find:n=?
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Here is your answer-
________
let,
Sn = 3250
a = 305
d = -15
n = ?
By general formula for Sn ....
Sn = n/2 [ 2a + (n-1) d ]
3250 = n/2 [ 2 × 305 + (n-1) -15
3250 × 2 = n [ 610 -15n + 15 ]
6500= n [ 625 - 15n ]
6500 = 625n - 15n^2
15n^2 - 625n + 6500 = 0
By factorization ___
( 3n - 65 ) ( 5n - 100 ) = 0
3n - 65 = 0 or 5n - 100 = 0
3n = 65 or 5n = 100
n = 65/3 or n = 100/5
Therefore,
n= 100/5
n = 20
Hope Helpful ______
___Pls Mark it as a Brainlist ____
Here is your answer-
________
let,
Sn = 3250
a = 305
d = -15
n = ?
By general formula for Sn ....
Sn = n/2 [ 2a + (n-1) d ]
3250 = n/2 [ 2 × 305 + (n-1) -15
3250 × 2 = n [ 610 -15n + 15 ]
6500= n [ 625 - 15n ]
6500 = 625n - 15n^2
15n^2 - 625n + 6500 = 0
By factorization ___
( 3n - 65 ) ( 5n - 100 ) = 0
3n - 65 = 0 or 5n - 100 = 0
3n = 65 or 5n = 100
n = 65/3 or n = 100/5
Therefore,
n= 100/5
n = 20
Hope Helpful ______
___Pls Mark it as a Brainlist ____
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