The first and the last terms of an AP are 7 and 49 respective . if sum of all it's terms is 420, find its common difference.
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Hey
Given that :-
a = 7
l = 49
Sum = 420
A / q ,
n / 2 ( a + l ) = 420
=> n ( 7 + 49 ) = 420 * 2
=> 56 * n = 420 * 2
=> n * 8 = 60 * 2
=> n * 2 = 15 * 2
=> n = 15 .
Now ,
a + ( n - 1 ) d = 49
=> 7 + ( 15 - 1 ) d = 49
=> 14 d = 42
=> d = 3 .
thanks :)
Given that :-
a = 7
l = 49
Sum = 420
A / q ,
n / 2 ( a + l ) = 420
=> n ( 7 + 49 ) = 420 * 2
=> 56 * n = 420 * 2
=> n * 8 = 60 * 2
=> n * 2 = 15 * 2
=> n = 15 .
Now ,
a + ( n - 1 ) d = 49
=> 7 + ( 15 - 1 ) d = 49
=> 14 d = 42
=> d = 3 .
thanks :)
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