The average weight of a group of boys is 20 kg. After a boy of weight 25 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) 7.0 B) 5.0 C) 6.0 D) 4.0 E) 8.0
Let the number off boys in the group originally be x.   Total weight of the boys = 20x   After the boy weighing 25 kg joins the group, total weight of boys = 20x + 25   So 20x + 25 = 21(x + 1) = &gt; x = 4.   Answer: 4.0
<result>D</result>
The average weight of a group of boys is 20 kg. After a boy of weight 25 kg joins the group, the average weight of the group goes up by 1 kg. Find the number of boys in the group originally ?