Question

How may days does a bag of 1.5kg oat some last if you use 50g

Answer 1

The prefix "kilo" means thousand, so a kilogram is a thousand grams.
1,000 / 50 = 20   1 kg would last 20 days, and 1/2 kg would last 10 days.
20 + 10 = 30    1.5 kg would last 30 days if you used 50 g a day.