i borrowed 500 rupess from each of my two friends 250+250 = 500 i bought a shirt of 450 that is 500-450= 50 i lost 30 rupees that is 50-30 = 20 i returned 10 rupees to my one friend and 10 rupees to the other to whom i borrowed 250 and 250 now as i gave them 10 and 10 back now i owe them 240 and 240 if we calculate 240+240= 480+30 that i lost equals to 240+240+30 = 510 when i borrowed only 500 where from these 10 rupees came..