25 magical fruits remain. After 10 check points Birbal loses a total of 30 fruits (3*10) die to the presence of 3 sacks. Now, he places the remaining 60 fruits in 2 sacks to ensure minimal tax payment. After another 15 check points he loses another 30 (15*2) fruits. So he packs the remaining fruits into 1 sack. Only 5 check points are left now, so he loses another 5 fruits. Hence 25 fruits are left {90-(30+30+5)}