Let 
be the 20 marks of the boys, and 
be the 10 marks of the girls.
We know that the global mean was 70, meaning that
Multiplying both sides by 30 we deduce that the sum of the scores of the whole classroom is
By the same logic, we work with the marks of the boys alone: we know the average:
And we deduce the sum of the marks for the boys:
Which implies that the sum of the marks of the girls is 
And finally, the mean for the girls alone is
Answer: N=-4
Step-by-step explanation:
STEP
1
:
STEP
2
:
Pulling out like terms
2.1 Pull out like factors :
-4n - 9 = -1 • (4n + 9)
Equation at the end of step
2
:
-3 • (4n + 9) - 21 = 0
STEP
3
:
STEP
4
:
Pulling out like terms
4.1 Pull out like factors :
-12n - 48 = -12 • (n + 4)
Equation at the end of step
4
:
-12 • (n + 4) = 0
STEP
5
:
Equations which are never true:
5.1 Solve : -12 = 0
This equation has no solution.
A a non-zero constant never equals zero.
Solving a Single Variable Equation:
5.2 Solve : n+4 = 0
Subtract 4 from both sides of the equation :
n = -4
One solution was found :
n = -4
Answer:
b I do believe good luck with the answer
Go 6 units in X axis and 1 unit in Y axis and you get V.
Alternative B
Is that 21/2 or 1/2 huh
elephant grass grows to 9/2 inches in 9 days
elephant grass grows to 4.5 inches in 9 days
