Question

Find the sum of the three middle terms of the AP; 18,15 1/2,13......(-47)

Answer 1

Answer:

-43.5

Step-by-step explanation:

AP

a = 18

d = $15\frac{1}{2} - 18$

=> d = $\frac{31}{2} -18$

=> d = $-\frac{5}{2}$

=> d = -2.5

Last term = -47

Let say there are n terms

nth term = a +(n-1)d = -47

=> 18 + (n-1)(-2.5) = -47

=> (n-1)(-2.5) = -65

=> (n-1) = 26

=> n = 27

Middle term = (27+1)/2 = 14th term

Three middle term then  13th , 14th & 15th Term

13th term = a +12d

14th term = a +13d

15th term = a + 14d

Sum of 13th , 14th & 15th Term = 3a + 39d

= 3*(18) + 39(-2.5)

= 54 - 97.5

= - 43.5

Answer 2

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