Where are four athletes in a relay team. the masses of three of these athletes are
32.5kg, 47.8kg and 53.9kg respectively. calculate, in kg
the total mass of these three athletes
ii. the mass of the fourth athlete if the mean mass of the relay team is
50.9kg

Step-by-step explanation:

Total just means adding all the different ones up, so the first answer is adding the three first athletes.

Mean is taking the total (line in the last part) and then dividing by the number there are.  Here we add a fourth athlete we don't know the mass of.  So we don't know the total.  if we say the unknown's athlete's  mass is x then the new total is 32.5 + 47.8 + 53.9 + x.  Now you can set up the average, which we know the answer to.  So you divide the total by 4 since there are four atheltes, and the question tells us this problem equals 50.9.  Can you figure out how to use algebra to find this x?  If not I can explain further.