Question

How many terms of the progression 15, 12, 9, 6,
...........should be taken so that their sum is 36?

Interpret the double answer.​

Answer 1

Answer:

3 and 8

Step-by-step explanation:

15+12+9 and 15+12+9+6+3+0+-3+-6

Answer 2

Answer:

n = 3 or n = 8

Step-by-step explanation:

from the given A. P. we get

first term, a = 15

common difference, d = -3

sum of n terms, Sn= 36

number of terms, n = ?

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

36=n/2(2 x 15+(n-1)(-3))

36=n/2(30+3-3n)

36 x 2=n(33-3n)

72= 33n - 3n2

3n2 - 33n +72 =0

by simplifying

n2 - 11n + 24= 0

n2 -8n -3n +24 =0

n(n-8) -3(n-8) = 0

(n-8)(n-3)= 0

=>n-8=0 or n-3=0

so, n=8 or n=3