Lesson 3: Unknown Values (Mean)

What is an unknown value in a mean question? A question that asks for the unknown value in a data set.

This is an example of an unknown value mean question:

Katie buys 6 hair ties. These are the costs of the hair ties: 16,19,22,30.50,41.50,___The mean price is 25.50. What is the cost of the 6th hair tie?

There are two ways to solve this problem:

Trial and Error: Add up all of the known values. Divide by the number of units (in this case, hair ties). Trial and Error the unknown value until you reach the correct mean. Check your work.

16+19+22+30.50+41.50= 129

Unknown value: 24

Checking:

16+19+22+30.50+41.50+24= 153

153/6= 25.50

Checking:

16+19+22+30.50+41.50+24= 153

153/6= 25.50

Backwards: Add up all of the known values. Multiply the number of units (in this case, hair ties) by the mean. Subtract the known values from the product of the units and mean. Check your work.

Example:

16+19+22+30.50+41.50= 129

25.50x6= 153

153-129= 24

Checking:

16+19+22+30.50+41.50+24= 153

153/6= 25.50

25.50x6= 153

153-129= 24

Checking:

16+19+22+30.50+41.50+24= 153

153/6= 25.50