Answer:
20 gallons were used from the tank with the octane rating of 80.
Step-by-step explanation:
Given : One tank of gasoline has an octane rating of 140 and another tank of gasoline has an octane rating of 80. To obtain a mixture of 60 gallons with an octane rating of 120.
To find : How many gallons should be used from the tank with the octane rating of 80?
Solution : Let x be the volume of gas whose octane rating is 140 and
y be the volume of gas whose octane rating is 80.
Then, we form the equation as:
(1) 

or
.........[3]
(2) 
Now multiply equation (2) by 4
...........[4]
Subtract (4) from (3)



Put x in equation [4] we get,





Therefore, x=40 and y=20
So, 20 gallons were used from the tank with the octane rating of 80.
Answer:
the cost of one hot chocolate is $2.
Step-by-step explanation:
Let x be the hot chocolate cost and y be the newspaper cost.
Given:
A newspaper and three hot chocolates cost $7
So, the equation is
--------(1)
Two newspapers and two hot chocolates cost $6
So, the second equation is.
---------(2)
Find one hot chocolate cost?
Solve equation 1 for y.


Put y value in equation 2





negative sign is cancelled both side.


Therefore, the cost of one hot chocolate is $2.
Its asking for the units being used so the answer is Inches
Answer:
(1, –5)
Step-by-step explanation:
It is relatively easy to try the offered solutions to see what works.
<u>(1, -5)</u>
3(1) +10(-5) = -47 . . . true
5(1) -7(-5) = 40 . . . true
(1, -5) is the solution
_____
As a check, you can try some of the other choices:
<u>(1, 5)</u>
3(1) +10(5) ≠ -47
<u>(-1, -5)</u>
3(-1) +10(-5) ≠ -47
<u>(-1, 5)</u>
3(-1) +10(5) ≠ -47
None of the other choices works in the first equation, so they're not the solution.
The value of the constant k when the value of x and y is 7 and 3 respectively in the equation xy=k is 21.
<h3>What is an equation?</h3>
An equation is formed when two equal expressions are equated together with the help of an equal sign '='.
The value of the constant k when the value of x and y is 7 and 3 respectively in the equation xy=k can be written as,

Hence, the value of the constant k when the value of x and y is 7 and 3 respectively in the equation xy=k is 21.
Learn more about Equation:
brainly.com/question/2263981