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Math problem: How to express cost-saving potential in % when the quantity needed is unknown?

Q: Imagine you are a factory producing apple extract for baking. 

You are considering switching from a local supplier to a foreign supplier in order to save cost. 

The cost for 1 ton of apples is $2K from the local supplier and $1K from the foreign supplier. You'll also need to pay 5% import fees for the foreign apples (based on total apple cost). The transportation cost for the local apples is $10/km/truck. Each truck can fit 10 tons of apples and each truck needs to drive 100 miles. For the foreign apples, it's $20/km/truck. Each truck can also fit 10 tons but the truck needs to drive 200 miles. In addition to that there are 5% losses of the product during production from the local apples, but 10% for the foreign apples. 

What would be the cost difference expressed in % (the total number of tons of apples needed per year is unknown)? 

I know how to calculate the % difference in cost for the apples, but I do get stuck when it comes to considering the transportation, losses, and import fees. Any tips are appreciated! 

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Top answer
Pedro
Coach
on Oct 02, 2021
Bain | EY-Parthenon | Former Principal | 1.5h session | 30% discount 1st session

It seems you are trying to get to the overall % of savings by calculating the % difference for each type of cost. That is not the best way to do it (to be honest, not the right way to do it).

You should calculate the total cost for each option and then calculate the cost difference. So here you go, assuming I got the prompt right:

Cost = (Purchase price + Import duty + transportation cost) / (1-%losses)

  • Domestic = [$2000 + ($10*100km/10tons)] / (1-5%losses) = (2000 + 100) / 0,95 = ~$2210 (or $2200 for simplification purpose)
  • Foreign    = [$1000 * (1+5%imp) + ($20*200km/10tons)] / (1-10%losses) = ($1000 + $50 + $400) / 0,9 = ~1611 (or $1600 for simplification purpose).
  • Savings = ($2200-$1600)/$2200=$600/$2200= ~27%
Ian
Coach
on Oct 03, 2021
Top US BCG / MBB Coach - 5,000 sessions |Tech, Platinion, Big 4 | 9/9 personal interviews passed | 95% candidate success

Hi there,

Just to add to Pedro's great answer, you need to structure and lay out your math.

Pratice breaking down complicated math problems into the things you need to calculate and the things you know. Think through the struture before diving into all of the numbers! Make sense?

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