Answer:
?? = 900
Explanation:
Solve algebraically
let x be ball and y be cube
x + y = 100
x - y = 80
xy = ??
We can solve by elimination. Eliminate one of the variables by adding OR subtracting the entire equations. I will add.
. x + y = 100
+ x - y = 80 y + - y = y - y = 0; The variable is eliminated
. 2x = 180 Divide both sides by 2 to isolate x
. x = 90
Substitute x = 90 into one of the equations.
x + y = 100
90 + y = 100 Isolate y by subtracting 90 from both sides
y = 100 - 90
y = 10
Find xy = ?? by substituting y for 10 and x for 90.
xy = (90)(10) = 900
Therefore the value of ?? is 900.