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Answer: 525
Step-by-step explanation:
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Step-by-step explanation:
21 + 23 + .......... + 49
Now , As you can see it's AP ( Arithmetic Progression ) with following :-
a = 21
d = 2
tn = 49
Now, use these values in the formula :-
tn = a + ( n - 1 ) d
49 = 21 + ( n - 1 ) 2
49 = 21 + 2n - 2
49 = 19 + 2n
49 - 19 = 2n
30 = 2n
30 / 2 = n
Therefore , n = 15
Now,
S 15 = 15 / 2 ( 2 ( 21 ) + ( 15 - 1 ) 2 )
= 15 / 2 ( 42 + 28 )
= 15 / 2 ( 70 )
= 15 × 35
= 525
hope it helps you mark as brainliest please