Find the Sum of those integers from 1 to 500 which are multiples of 2 as well as of 5.


Since, multiples of 2 as well as of 5 = LCM of (2, 5) = 10


Multiples of 2 as well as of 5 from 1 and 500 is 10, 20, 30, …., 500.


Clearly this is an AP with common difference, d = 10


And first term, a = 10


Let the no if terms in this AP are n


Then,


an = a + (n - 1)d


500 = 10 + (n - 1)10


490 = (n - 1)10


n - 1 = 49


n = 50


now, Sum of this AP


[ as last term is given]



= 25[ 10 + 500]


= 25(510)


= 12750


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