I will assume that this is national food delivery service. Assume 120M house-holds in U.S. Not everyone wants to use this service. Many people will like to go and pick their own vegetables given time permits. Majority of the U.S population lives is small cities and would probably shop for their own food.
For Calculating the # of trucks = Food demand/(Capacity of trucks multiplied by # of trips in a day)
Assumption; 20% of house holds use this service. – 24M.
I will categorize the 24 M households into two type based on the frequency of orders
Once a week – Small families – Working couples, consumers who cook their own food etc. let’s assume 40% of families fall in this category. (10M)
Twice a week – Family of four. Wants fresh ingredients so order more frequently. 60% of Households (14M)
Demand of groceries
Let’s assume that each person eats 5 pounds of food each week.
Once a week food demand per family= 5 x 2 people per family = 10 pounds each week
Weekly demand from all families = 10 x 10 = 100 M pounds of food
Twice a week order size per family = 5 x 3 people x 2 = 30 pounds each week
Weekly demand from all families = 30 x 14 = 420 M pounds of food
Total food requested = 420 + 100 = 520 M pounds.
I will shave this demand by 30% as sometimes their are left over food, traveling, eating out.
So total demand = 70 % of 520 = 350 M pounds (roughly)
Assume capacity of a truck = 1000 pounds.
Assume number of trips each day = 4
Truck required = 350 M/(1000 x 4) = 9K trucks nationally.