All Algebra 1 Resources
Example Questions
Example Question #4 : Direct Proportionality
If an object is hung on a spring, the elongation of the spring varies directly with the mass of the object. A 33 kilogram object increases the length of a spring by exactly 6.6 centimeters. To the nearest tenth of a kilogram, how much mass must an object posess to increase the length of that same spring by exactly 10 centimeters?
Let be the mass of the weight and the elongation of the spring, respectively. Then for some constant of variation ,
.
We can find by setting :
Therefore .
Set and solve for :
kilograms
Example Question #1 : How To Find Direct Variation
If is directly proportional to and when at , what is the value of the constant of proportionality?
The general formula for direct proportionality is
where is the proportionality constant. To find the value of this , we plug in and
Solve for by dividing both sides by 12
So .
Example Question #3 : How To Find Direct Variation
The amount of money you earn is directly proportional to the nunber of hours you worked. On the first day, you earned $32 by working 4 hours. On the second day, how many hours do you need to work to earn $48.
The general formula for direct proportionality is
where is how much money you earned, is the proportionality constant, and is the number of hours worked.
Before we can figure out how many hours you need to work to earn $48, we need to find the value of . It is given that you earned $32 by working 4 hours. Plug these values into the formula
Solve for by dividing both sides by 4.
So . We can use this to find out the hours you need to work to earn $48. With , we have
Plug in $48.
Divide both sides by 8
So you will need to work 6 hours to earn $48.
Example Question #4 : How To Find Direct Variation
The volume of a fixed mass of gas varies inversely as the atmospheric pressure, as measured in millibars, acting on it, and directly as the temperature, as measured in kelvins, acting on it.
A balloon is filled to a capacity of exactly 100 cubic meters at a time at which the temperature is 310 kelvins and the atmospheric pressure is 1,020 millibars. The balloon is released, and an hour later, the balloon is subject to a pressure of 900 millibars and a temperature of 290 kelvins. To the nearest cubic meter, what is the new volume of the balloon?
If are the volume, pressure, and temperature, then the variation equation will be, for some constant of variation ,
To calculate , substitute :
The variation equation is
so substitute and solve for .
Example Question #4 : How To Find Direct Variation
The monthly cost to insure your cars varies directly with the number of cars you own. Right now, you are paying $420 per month to insure 3 cars, but you plan to get 2 more cars, so that you will own 5 cars. How much does it cost to insure 5 cars monthly?
The statement, 'The monthly costly to insure your cars varies directly with the number of cars you own' can be mathematically expressed as . M is the monthly cost, C is the number of cars owned, and k is the constant of variation.
Given that it costs $420 a month to insure 3 cars, we can find the k-value.
Divide both sides by 3.
Now, we have the mathematical relationship.
Finding how much it costs to insure 5 cars can be found by substituting 5 for C and solving for M.
Example Question #211 : Functions And Lines
Does the equation below represent a direct variation? If it does, find the constant of variation.
No,
Yes,
Yes,
No,
Yes,
Yes,
Direct Variation is a relationship that can be represented by a function in the form
, where
is the constant of variation for a direct variation. is the coefficient of .
The equation is in the form , so the equation is a direct variation.
The constant of variation or is
Therefore, the answer is,
Yes it is a direct variation, with a direct variation of
Example Question #212 : Functions And Lines
Suppose and , and that is in direct proportion with . What is the value of proportionality?
The general formula for direct proportionality is
where is our constant of proportionality. From here we can plug in the relevant values for and to get
Solving for requires that we divide both sides of the equation by , yielding
Example Question #5 : How To Find Direct Variation
The cost of a catering company varies directly with the number of people attending. If the cost is $100 when 20 people attend the party, find the constant of variation.
Because the cost varies directly with the number of people attending, we have the equation
Where is the cost and is the number of people attending.
We solve for , the constant of variation, by plugging in and .
And by dividing by 20 on both sides
Yields
Example Question #211 : Functions And Lines
The amount of money Billy earns is directly proportional to his hours worked. Suppose he earns every eight hours of work. What is the minimum hours Billy must work in order to exceed ? Round to the nearest integer.
Write the formula for direct proportionality.
Let:
Substitute twelve dollars and eight hours into this equation to solve for .
Divide by eight on both sides.
Substitute back into the formula.
To find out the minimum number of hours Billy must work to make , substitute into and solve for .
Multiply by two thirds on both sides.
Simplify both sides.
Billy must work at least hours to earn as much required.
Example Question #1 : How To Find The Nth Term Of An Arithmetic Sequence
The first term of an arithmetic sequence is ; the fifth term is . What is the second term?
To find the common difference , use the formula .
For us, is and is .
Now we can solve for .
Add the common difference to the first term to get the second term.