The mean weight of 75 2nd graders is 55.7 lbs and
the mean weight of 25 1st graders is 42.6 lb.
What is the mean weight of the 100 children
First you must ask yourself what is mean weight? It is the average weight. So let's take the 2nd graders for example. To find the mean weight, they took the weight of 75 2nd graders, added it all together and divided by 75. To find the total weight of the 2nd graders, you would multiple the average weight by 75. Do you understand? You're simply to the opposite to get back to where you started.
2nd Graders Total Weight: 55.7 x 75 = 4177.5 lbs
1st Graders Total Weight: 42.6 x 25 = 1065
Now what you can do is add the total weights of both grades and divide by 100 to get the mean weight of the 100 children! :)