1.

the 1st term of an Ap is 5 and last term is 45 and sum is to 400 find number of terms and common difference

Answer»

Given,
First term ( a ) = 5
Last term ( l) = 45
Sum of n terms = 400 .

We KNOW that,
Sum of n terms = n/2 ( a + l)

400 = n/2 ( 5 + 45 )

400/50 =n/2

8 = n/2

8 * 2 = n.

n = 16 .

So, 16 th term = 45

a + 15 d = 45

5 + 15d = 45

15d = 40

d = 8/3 .

SECOND term = a + d = 5 + 8/3 = 23/3

Common difference = 8/3

HOPE HELPED !


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