"Durability" is the measure of how long a certain appliance remains functional without breaking down. Sixty years ago, average refrigerator durability was 15 years, whereas now refrigerators operate continuously for more than 40 years on average. Thus, at that time, people must have considered refrigerators to be nearing the end of their operational life at an age that we now consider will leave many more working years.

Which of the following, it true, undermines the argument above?

A. Today, many more households own refrigerators than did households sixty years ago.
B. Most of the improvements in durability in the past sixty years have been achieved through cutting down on the number of refrigerators that break down in the first year of ownership.
C. May of the refrigerators that last an extremely long time today do so only because of engineering technology that was not available thirty years ago.
D. The proportion of refrigerators that break down when they are between 35 years and 40 years old is significantly smaller today than is the proportion of refrigerators that break down after 40 years.
E. More refrigerators sixty years ago received regular service than receive it today.

Solution is B. I chose E. I understand why E is wrong after reading the Explanation but can't really see why B is correct.

This one is pretty subtle. The stimulus gives us information about average durability; how would we calculate that? A good way would be to add up the lifespan of each refrigerator and divide by the number of refrigerators.

B essentially says that the increase in durability is due to eliminating the refrigerators that die in the first year of use. If we think back to our formula, these would be the lifespans that drag down the average. If we can eliminate those low numbers, the average will naturally increase.

How does thus undermine the conclusion? The conclusion says they people 60 years ago must considered a 15-year-old fridge to be nearly out of operation. Choice B implies that once that fridge made it past its first year of use, it was likely to have a long lifespan. Thus, people with a 15-year-old fridge probably would not consider it near the end of its operational life.

Bill