Answer:
The correct answer is OB.
Step-by-step explanation:
Let us recall the Associative Property of Addition: given three real numbers ,
and
the following equality holds:
.
Let us remark that the Associative Property of Addition tells us that we can perform the sums in any order. So,
.
In the other options there was used the Commutative Property of Addition.
Answer:
First brand of antifreeze: 21 gallons
Second brand of antifreeze: 9 gallons
Step-by-step explanation:
Let's call A the amount of first brand of antifreeze. 20% pure antifreeze
Let's call B the amount of second brand of antifreeze. 70% pure antifreeze
The resulting mixture should have 35% pure antifreeze, and 30 gallons.
Then we know that the total amount of mixture will be:
Then the total amount of pure antifreeze in the mixture will be:
Then we have two equations and two unknowns so we solve the system of equations. Multiply the first equation by -0.7 and add it to the second equation:
+
--------------------------------------
We substitute the value of A into one of the two equations and solve for B.