Question

find the sum of the series 72+70+68+..........+40 . what will be rhe sum if all the sums are increased by 12.5%​

Answer 1

Answer:

99..................

Answer 2

Answer:

original sum = 952 ; new sum = 1071

Step-by-step explanation:

72+70+68.........+40

It's an AP

a = 72

d = 70-72 = -2

let nth term of this ap be 40

40 = a +(n-1)d

40 = 72 (n-1)(-2)

40 = 72 -2n +2

2n = 74-40

2n = 34

n = 17

Sn = n/2 {2a + (n-1)d}

= 17/2 { 144-32}

= 17/2(112)

= 56× 17 = 952

Now , when each no. is increased by 12.5% , then the sum of this AP will also be increased by 12.5 % i.e new sum will become 112.5% of the original sum

New sum = 112.5(Sn)/100

= (112.5×952)/100

= 1071