The average weight of a group of boys is 30 kg. After a boy of weight 39 kg joins the group, the average weight of the group goes up by 1 kg. Find the number of boys in the group originally ? Choose the most appropriate option.
A) A)4 B) B)8 C) C)6 D) D)2 E) E)1
Let the number off boys in the group originally be x.   Total weight of the boys = 30x   After the boy weighing 39 kg joins the group, total weight of boys = 30x + 39   So 30x + 39 = 31(x + 1) = &gt; x = 8.   Answer:8
<result>B</result>
The average weight of a group of boys is 30 kg. After a boy of weight 39 kg joins the group, the average weight of the group goes up by 1 kg. Find the number of boys in the group originally ?