An Apple iPhone 6 smart phone can be bought now for $999. An Android Samsung Galaxy 5 smart phone can be bought now for $599.
If the Samsung phone lasts for four years, approximately how long must the Apple phone last for to have the same equivalent annual cost?
Assume that both phones have equivalent features besides their lifetimes, that both are worthless once they've outlasted their life, the discount rate is 10% pa given as an effective annual rate, and there are no extra costs or benefits from either phone.