Assuming that the total price is 20% profit, the cost of a commodity is:
[253-200× (1+20%)] (30%-20%) =130 (yuan)
(2) Original price of cantaloupe:
42 ÷ [(1-20%) × 3+(1-20%) × (1-20%) × 5] = 7.5 (yuan)
If all eight honeydew melons were bought on the third day:
7.5× (1-20% )× (1-20% )× (1-20% )× 8 = 30.72 (yuan)