The mean mass of a group of N people is 75 kg.
Jim, Karen and Leroy join this group, without anyone leaving; the new mean mass is 78 kg.
The mean mass of Jim, Karen and Leroy is 90 kg.
What is the value of N?
Answer:
8) B
Average mass of first group = 75 kg
Total mass if group of N people = 75 x N = 75N
Three people join the group. Total number of people now = N + 3
Average mass now = 78
Total mass now = 78 (N + 3) = 78N + 234
Average mass of the three people = 90 kg
Total mass of three new people = 90 x 3 = 270 kg
Total mass of new group = Total mass of initial group + Total mass of three new people
78N + 234 = 75N + 270
78N ā 75N = 270 ā 234
3N = 36
N = 12
