In the last two years, each of Jeremy’s six children grew in height by at least one inch. If the standard deviation of their heights two years ago was 4.5 inches, what is the standard deviation of their heights?

We are given a set with 6 terms and the standard deviation of 4.5. Next, we are told that each term of this set was increased and are asked to find the new standard deviation of this changed set.

(1) In the last two years, the heights of Jeremy’s six children have increased a total of 17 inches. Not sufficient, since many different scenarios of increase of each data point are possible.

(2) In the last two years, each child’s height has increased by 5 percent. Important property: if we increase or decrease each term in a set by the same percent (multiply all terms by the constant): SD will increase or decrease by the same percent. So, since each of 6 terms has increased by 5% then the standard deviation of 4.5 would also increase by 5% and become 4.5*1.05. Sufficient.

Answer: B.
_________________

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________