James bought a few hamsters. For each day after the first day of the week, the hamsters ate 20 grams of food more than the previous day. The hamsters grew fast, finishing 1260 grams of food in the first week. How much food did the hamster eat on the first day?

Answer 1

the last day is six days from the first day

1st day = f

last day = f + 6(20) = f + 120

arithmetic series average = (1st + last) / 2 = (2 f + 120) / 2 = f + 60

for 7 days ... food = 7(f + 60) = 7 f + 420 = 1260
... 7 f = 840 ... f = ?