Question

find the sum of 20 term of an ap which d = 5 and the 11 th term is 55 total sum​

Answer 1

Answer:

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Answer 2

Step-by-step explanation:

Given:-

d=5

11th term=55

To find:-

Find the sum of 20 terms ?

Solution :-

Common difference of an AP=(d)=5

11 th term (t 11)= 55

we know that tn=a+(n-1)d

=>t 11=a + (11-1) (5)

=>55= a+10(5)

=>55=a+ 50

=>a=55-50

=>a=5

First term (a)=5

we know that Sn =(n/2)[2a+(n-1)d]

we have ,n=20

=>S20 = (20/2)[2(5)+(20-1)(5)]

=>S20 = 10[10+19(5)]

=>S20= 10[10+95]

=>S20=10(105)

=>S20=1050

Therefore,S20=1050

Answer:-

The Sum of 20 terms of the given AP =1050

Used formulae:-

If the first term "a" , Common difference "d" and number of terms "n" of an AP then

General or nth term =tn=a+(n-1)d

Sum of n terms =Sn=(n/2)[2a+(n-1)d]