bumblebee123
Junior Member
- Joined
- Jan 3, 2018
- Messages
- 200
After many attempts, I still can't get the right answer to this question. Can anyone tell me where I'm going wrong?
Question: the 12th term of an arithmetic series is 27
the 18th term of the arithmetic series is 45
a) find the sum of the first 60 terms of this arithmetic series
b) find the three consecutive terms in this arithmetic series whose sum is the same as the sum of the first 60 terms of the series
I started off by using simultaneous equations to find the value of the common difference ( d = 3 ) and the first term ( a = -6 ).
I plugged this into the formula for the sum of the first 60 terms in the series: Sn = n/2 [ 2a + ( n - 1 )d ]
S60= 60/2 [ 12 + 177 ]
S60= 30 x 189 = 5670
however this does not give me the right answer. The correct answer is: 4950
I haven't even started on the second question! does anyone know what to do? any help would be really appreciated
Question: the 12th term of an arithmetic series is 27
the 18th term of the arithmetic series is 45
a) find the sum of the first 60 terms of this arithmetic series
b) find the three consecutive terms in this arithmetic series whose sum is the same as the sum of the first 60 terms of the series
I started off by using simultaneous equations to find the value of the common difference ( d = 3 ) and the first term ( a = -6 ).
I plugged this into the formula for the sum of the first 60 terms in the series: Sn = n/2 [ 2a + ( n - 1 )d ]
S60= 60/2 [ 12 + 177 ]
S60= 30 x 189 = 5670
however this does not give me the right answer. The correct answer is: 4950
I haven't even started on the second question! does anyone know what to do? any help would be really appreciated