Missing Number Problems With Fractions & Decimals

Instructor: Cassandra Cook

Cassandra Cook has taught grades K-8 and has a Specialist degree in Curriculum and Instruction

This lesson will help you understand how to solve problems with missing numbers with fractions and decimals. Fractions and decimals are similar and can be used interchangeably.

Missing Number Problems with Fractions and Decimals

Missing number problems can seem difficult to do since there's a number missing. However, as long as you have enough information using the remainder of the problem, you can solve it.

What is a Fraction?

Fractions are numbers with parts to a whole. For example 3/5 means I have three parts out of a possible total of five parts. Three is my part and five is the whole. The part, or top number, is the numerator. The whole, or bottom number, is the denominator.

What is a Decimal?

Decimals are numbers shown using a decimal point (.). The decimal equivalent for 3/5 is .60. You would read .60 as six tenths or sixty hundredths.

All decimals and fractions are not whole numbers and both decimal and fractions can be converted interchangeably.

Using Fractions and Decimals with Missing Number Problems

As a world renowned bakery chef, you have to find the correct mixtures for a special cake. Unfortunately during your last project, the recipe book got wet and smeared the amounts. Now you're missing some key information! How do you mix the correct amounts? What numbers are missing? What will happen if the mixture isn't correct? Well not to worry because we will figure it out!

The first step says for you to mix 3/4 cups of flour with sugar. The total amount for the flour and sugar will be 1.50. Except you do not know how much sugar or why the answer is a decimal now. Let's figure it out:

3/4 + N= 1.50

  1. Convert 1.50 to a fraction with four as the denominator- 1.50= 1 1/2= 1 2/4
  • Since we have 3/4 cup of flour, we want to use fourths as the denominator to make solving the problem more fluent by having common denominators.
  1. Change the decimal into a improper fraction- 1.50= 1 2/4= 6/4
  • The whole is 4 because it is the denominator
  • 4/4 equals 1 and there are 2/4 left over.
  • 2/4 equals .50 for half. 4/4+2/4=6/4
  1. 6/4- 3/4= 3/4
  • 6-3=3 and the denominator stays the same

You will need 3/4 cup of sugar for this recipe to mix with 3/4 cup of flour.

Converting Fractions and Decimals

When using decimals, the place value of the decimal lets you know the denominator for the equivalent fraction. The first place value after a decimal is the tenths. When reading a decimal with just one number after the point it is read as tenths. For example .3 is three tenths. If you have a decimal with two numbers after the point it is read as hundredths. For example .03 is three hundredths and it is not the same as .3. A decimal number such as .65 is sixty-five hundredths.

When you say the place value for the decimal number, you are also indicating the denominator for the part to whole. If I have .3 the fraction is 3/10, this reads three tenths, exactly the same as .3. If we use .65 it reads sixty five hundredths and the fraction is 65/100 which reads exactly the same as .65.

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