the sum of 10th and 11th terms of an arithmetic sequence is 65.what is it's common difference ?
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GIVEN
the sum of 10th and 11th terms of an arithmetic sequence is 65.
TO FIND
common difference (d)
SOLUTION
a10= a+9d ....1.
a11= a+ 10d .....2.
By adding equation 1 and 2
a10 + a11= 65
a+ 9d+ a 10d= 65
2a+ 19d= 65
19d= 65-2a
d= 65-2a/19
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