Maths

Plz the first and last term of an AP are 79 and -5 if the sum is 814. Find
A. The number of terms
B. Common difference.

1. 👍 0
2. 👎 0
3. 👁 195
1. http://www.mathsisfun.com/algebra/sequences-sums-arithmetic.html

XN = 79+d(N-1) = -5
814 = N/2[ 2(79) + (N-1)d ]

814 = N/2 [ 79 -5 ]

N = 1628/74
N= 22
then
-5 = 79 +d(21)
d = -84/21 = - 4

1. 👍 0
2. 👎 0
2. where is the last answer

1. 👍 0
2. 👎 0

Similar Questions

1. Maths

The 10th term of an a.p is -27 and the 5th term is -12 what is the 18th term? Find also the sum of its 25 term

2. algebra

The fifth term of an A.P exceeds twice the second term by 1.The tenth term exceeds twice the fourth term by 3. Find:1.the first term. 2.the common difference. 3.the sum of first twenty five terms.

3. maths

the sum of first 8 terms of an arithmetic progression is 156.the ratio of its 12th term to its 68th term is 1:5.calculate the first term and the fifteenth term. please help this questions please.

4. miss reiny correct-done

find the nth term of the series 1,3,6,11,19,31,48.... Hence duduce a formula for calculating the sum of the series plz help me show working

1. Arithmetic Progression

In an AP the 6th term is half the 4th term and the 3rd term is 15. a. Find the fist term and the common difference. b. How many times are needed to give a sum that is less than 65?

2. Math

The first term of GP exceed the second term by 2 and the sum to infinity is 15 find the series and the sum of first 5 term

3. LIVING ENVIRONMENT

the ability to grow in size is a characteristic of living organism .Although an icicle may grow in size over time,it is considered nonliving because there is 1)an incerase in matter ,but no increase in the number of icicle. 2)an

4. MATH

AN AP has 21 term the sum of 10 ,11,12 term is 129 and sum of last 3 term is 237.find AP

1. Arithmetic progession

The third term of an A.P is 10times more than the second term. Find the sum of the eight and fifteen term of the A.P if the seventh term is seven times the first term

2. Mathematics

The sum of the first 10 terms of an Ap is 145 and the sum of its fourth and ninth is 5 times the third term determine the first term and the constant difference

3. MATH

THE 14TH TERM OF AP IS 96 WHILE THE 25TH TERM IS 173 FIND THE A.19TH TERM B.SUM OF 13TH AND 56TH TERM

4. math

The second term of a GP is 81 and the fourth term is 9. Find, (i) the common ratio, (ii) the sum of the first terms, (iii) the sum to infinity.