Question

1)Find the sum of the series: 5+7+9+10+13+13+17+16+---- upto 40 terms.

Answer 1

Answer:

Step-by-step explanation:

5+7+9+10+13+13+17+16_____40 terms we are given

Let a and d be the first term and common difference

Now splitting the AP in two parts

S1 = 5+9+13+17 (a=5,d=4)

S2 = 7+10+13+16(a=7,d=3)

Sum for 40 terms=sum of 20 terms and sum of another 20 terms

S = n/2 (2a+(n-1)d)+n/2 (2a+(n-1)d)

S = 20/2 (2×5+(20-1)4)+20/2(2×7+(20-1)3)

S = 10 (10+19×4)+10 (14+19×3)

S =10×10+76+10×14+57

S =10×86+10×71

S =860+710

S =1570

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