The sum to n terms (Sequences and Series) question (1 Viewer)

[BlueGas]

I need help with this question. The sum of the first 10 terms of an arithmetic series is 100 and the sum of the next 10 terms is 300. Find the series.

 

[Silly Sausage]

< - equation 1
< - equation 2
Solving simultaneously
< - equation 2
minus < - equation 1x2
-------------------------
, d = 1 and a is 11/2

 

[BlueGas]

< - equation 1
< - equation 2
Solving simultaneously
< - equation 2
minus < - equation 1x2
-------------------------
, d = 1 and a is 11/2

The answer is 1, 3, 5, 7, ... so d can't be 1 and a can't be 11/2.

 

[InteGrand]

< - equation 1
< - equation 2
Solving simultaneously
< - equation 2
minus < - equation 1x2
-------------------------
, d = 1 and a is 11/2

The Equation 2 here should have 400 on the LHS, because the question says the "next" 10 terms have sum 300, so the first 20 terms in total have sum 100+300 = 400.

And 20 - 1 instead of 10 - 1.

 

[VBN2470]

Sum of first 10 terms is 100 and sum of next 10 terms is 300, which means sum of the first 20 terms is 400. So you would have:


Solve simultaneously to get a=1 and d=2. Hence, the series is

1+3+5+7+...

 

[BlueGas]

The Equation 2 here should have 400 on the LHS, because the question says the "next" 10 terms have sum 300, so the first 20 terms in total have sum 100+300 = 400.

And 20 - 1 instead of 10 - 1.

Sum of first 10 terms is 100 and sum of next 10 terms is 300, which means sum of the first 20 terms is 400. So you would have:


Solve simultaneously to get a=1 and d=2. Hence, the series is

1+3+5+7+...

Thanks lads.

 

[Silly Sausage]

shit lol sry