The number of ordered pairs such that
is divisible by 5 is
1250
2000
2500
5000
Note that ends in
(corresponding to
and 4 respectively.)
Thus, cannot end in 5 for any values of
.
In other words, for to be divisible by 5 , it should end in 0 .
For o cnd in 0 , the forms of
and
should be as follows:
Thus, for a given value of there are just 25 values of
for which
ends in 0 . [For instance, if
, then
there are
ordered pairs
for which
is divisible by 5 .
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