To solve this problem, we'll start by using the information given to find the total mass of Mei Mei and her cousins.
Let's assume that Mei Mei has "x" cousins.
According to the problem, the average mass of Mei Mei and her cousins is 45 kg. This means that the sum of their masses divided by the total number of people (including Mei Mei) is 45 kg.
So, (Mei Mei's mass + total mass of her cousins) / (1 + x) = 45 kg.
Mei Mei's mass is given as 53 kg, so we can write the equation as:
(53 kg + total mass of her cousins) / (1 + x) = 45 kg.
Now, we are also given that the average mass of her cousins is 43 kg. This means that the sum of their masses divided by the total number of cousins is 43 kg.
So, total mass of her cousins / x = 43 kg.
We can write this equation as:
(total mass of her cousins) / x = 43 kg.
Now, we have two equations with two unknowns. We can solve this system of equations to find the values of "total mass of her cousins" and "x".
Equation 1: (53 kg + total mass of her cousins) / (1 + x) = 45 kg.
Equation 2: (total mass of her cousins) / x = 43 kg.
Let's solve Equation 2 for "total mass of her cousins":
(total mass of her cousins) = 43 kg * x.
Substituting this into Equation 1:
(53 kg + 43 kg * x) / (1 + x) = 45 kg.
Now we can solve for "x" by simplifying and solving the equation:
53 kg + 43 kg * x = 45 kg * (1 + x).
53 kg + 43 kg * x = 45 kg + 45 kg * x.
43 kg * x - 45 kg * x = 45 kg - 53 kg.
-2 kg * x = -8 kg.
Dividing both sides by -2 kg:
x = 4.
Therefore, Mei Mei has 4 cousins.