Homework Help: math

Posted by Janice - Please Help!!! on Thursday, April 7, 2011 at 12:00pm.

Find the exact value (either decimal or fractional form) of the first term of an arithmetic sequence if the sum of the first 100 terms is 7099.5 and the sum of the next 100 terms is 20799.

math - Mgraph, Thursday, April 7, 2011 at 12:47pm
We find a from a system:
a +a+99d =7099.5
a+100d+a+199d=20799

We subtract from the 2nd the 1st:

200d=13699.5
d=68.4975

2a+99x68.4975=7099.5
a=159.12375 (0.12375=99/800)
math - Steve, Thursday, September 22, 2011 at 12:42pm
Ummm.

Sn = n(a1 + an)/2
S100 = 100(a1 + a100)/2
= 50(a+a+99d)
= 100a + 4950

Answer this Question

Related Questions

MATH !!!!!!!!! HELP - Find the exact value (either decimal or fraction form) of ...
Math - Arithmetic & Geometric - 1) Given the terms a35 = 1238 and a70 = 1483...
Maths - 1..The first 2 terms of a geometric progression are the same as the ...
Math (11) - The sum of the first 16 terms of an arithmetic sequence is 23 times ...
AP and GP - 1) Given the terms a35 = 1238, a70 = 1483 of an AP. Find the exact ...
Precalculus - The 8th term in an arithmetic sequence is 5, and the sum of the ...
maths - 1) The first term of arithmetic progression is -20 and the sum of it'...
MATH - In an arithmetic sequence, the first term is 100 and the sixth term is 85...
Math - A sequence is formed by adding together the corresponding terms of a ...
Math - Arithmetic Sequences - The sum of the 4th and the 14th term of an ...

For Further Reading

First Name:
School Subject:
Answer: