Answer: 2 porters joined the group
Explanation:
First, you are told that "13 porters are carrying a total weight of 195kg". You can use this information to create an equation to find the average weight carried by each porter.
^195kg (total weight) divided by 13 (the number of porters) is equal to 15kg (the average weight carried by each of the 13 porters).
You are then told that "extra porters join the group, so they carry an average weight of 13 kg of baggage". because some porters joined the group, you'll have to add p (p = number of porters) to the original equation and change the average weight from 15kg to 13kg.
^195kg (total weight) divided by 13+p (total number of porters after some joined group) is equal to 13kg (new average weight)
You can then use your new equation to solve for "p" and find the number of porters added.
p = 2