Labels on jars are as follows
Jar 1 : Peanut butter
Jar 2 : Grape
Jar 3 : P.b. / Grape
Only one jelly bean from the p.b./grape jar will do the trick.
The trick here is to realize that every jar is mislabeled. Therefore you know that the peanut butter jelly bean jar is not the peanut butter jelly bean jar and the same goes for the rest.
You also need to realize that it is the jar labeled p.b./grape, labelled as the mix jar, that is your best hope. If you choose a jelly bean out of there, then you will know whether that jar is peanut butter or grape jelly jelly beans. It can’t be the mix jar because i already said that every jar is mislabeled.
Once you know that jar 3 is either peanut butter, or grape jelly, then you know the other jars also. If it is peanut butter, then jar 2 must be mixed because it can’t be grape (as its labeled) and it can’t be peanut butter (that’s jar 3). Hence jar 1 is grape.
If jar 3 is grape, then you know jar 1 must be the mix because it can’t be p.b. (as its labeled) and it can’t be grape (that’s jar 3). Hence jar 2 is peanut butter.
You just need to open any of the jelly beans jars (Ans is not just p.b./grape jar). If you open either of Jar1 or Jar2, even then you will be able to label the jars correct. So the correct ANSWER is any of the one jar needs to be opened.
Example if Jar 1 is opened:
Jar one will surely not contain p.b, so it could contain either grape or mix jelly beans.
a. If Jar 1 contains grape jelly bean, then jar 2 will contain mix jelly beans (as Jar 3 can’t have mix jelly beans in it, due to mislabeling) and jar 3 will contain peanut jelly beans
b. If Jar 1 contains mix jelly bean, then jar 3 will contain grapes jelly
beans (as Jar 2 can’t have grapes jelly beans in it, due to mislabeling)
and jar 2 will contain peanut jelly beans
Similarly, it can be explained IF JAR 2 IS OPENED.
😉
NICE One 🙂