What should be added to 6715 to get 815?
(a) 11115
(b) −11115
(c) 443
(d) 344
Let x be added to 6715 to get 815
⇒6715+x=815
⇒x=715−815
⇒x=9715−415
L.C.M. of 5 and 15 is 15
⇒x=9715−415×33
⇒x=9715−12315
⇒x=−2615
⇒x=−11115
Therefore, −11115 is the required number.
Hence, Option (b) is correct.