a man buys m no. of pens for rs. n each and sells n no. of pens for rs. m each. then what is the profit he have earned?	Choices
A) 0	B) 1	C) 2	D) 3	E) 4
c.p. of 1 pen=Rs n (given each)   so c.p. of m pens=rs mn   s.p. of 1 pen =rs m   so s.p. of n pens=rs mn   so profit =s.p.-c.p.=0(zero)   0NSWER:0
<result>A</result>
a man buys m no. of pens for rs. n each and sells n no. of pens for rs. m each. then what is the profit he have earned?