The average weight of a group of boys is 30 kg. After a boy of weight 40 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 correct choice:
A) 14	B) 5	C) 6	D) 7	E) 9
Let the number off boys in the group originally be x.   Total weight of the boys = 30x   After the boy weighing 40 kg joins the group, total weight of boys = 30x + 40   So 30x + 40 = 31(x + 1) = &gt; x = 9.   Answer: 9
<result>E</result>
The average weight of a group of boys is 30 kg. After a boy of weight 40 kg joins the group, the average weight of the group goes up by 1 kg. Find the number of boys in the group originally ?