Question

an AP if sum of 20 terms is 820 and first term is 3 then the common difference is
pls answer quickly

a) 2

b)4

c) 5

d) 1

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Answer 1

Answer:

b) 4

Step-by-step explanation:

Answer 2

$We \:know \: that ,$

$\boxed { \pink { Sum \:of \:n \:terms (S_{n}) = \frac{n}{2} [2a+(n-1)d }}$

$\blue { Where \: a = first \:term , \: d = Common \: differnce }\\\blue{ \: n = number \: of \: terms }$

$Here, a = 3 , n = 20\:and \: S_{20} = 820$

$S_{20} = 820$

$\implies \frac{20}{2} [ 2 \times 3 + (20-1)d] = 820$

$\implies 10 ( 6 + 19d) = 820$

$\implies 6 + 19d= \frac{820}{10}$

$\implies 6 + 19d= 82$

$\implies 19d= 82 - 6$

$\implies 19d= 74$

$\implies d= \frac{74}{19}$

$\implies d = 4$

Therefore.,

$Option \: \pink { ( b ) } \:is \: correct .$

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