an A.P.1st term is 1 and the last term is 149.The sum of all terms is 5625 then number of term is... *
1 point
150
149
74
75
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First term of AP, a = 5
Let no of terms be 'n' and common difference is 'd'
Last term of AP, an = 45
Given, sum of n terms = 400
And we know, sum of an AP if first term(a) and last term(an) is given,
Putting the values, we get,
⇒ 800 = 50n
⇒ n = 16
i.e. 16 terms are there and 16th term is last and equal to 45
Also, we know,
nth term of an AP,
Where, a and d are first term and common difference, respectively.
As, a16 = 45
⇒ a + 15d = 45
⇒ 5 + 15d = 45
⇒ 15d = 40
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