Question

An arithmetic sequence 6th term is 40and 10th term is 60.

a) what is the 13th term in this sequence
b) what is the total of first 25 terms

Answer 1

Answer: 75 and 1875

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Step-by-step explanation:

t 6 = 40

i.e. a+5d =40

or, a= 40-5d------>1

and, t 10 = 60

or, a+9d = 60

or, 40 -5d +9d = 60

or, 4d = 20

d=5

and, a = 40 - 5* 5 = 15

Now, 1.

t 13 =a + 12d = 15 +12 *5 = 75

2.

S = n⁄2 {2a + (n − 1) d}           where n= 25

 = 25/2 { 2* 15 + 24 * 5}

= 12.5 * 150

=1875