How much does a 7 month old weigh? (Subtraction/Regrouping/Conversions)

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My daughter, Hannah, recently had her seven-month birthday.  We have been taking a photo of her each month in her children's armchair with her giraffe stuffed animal, and putting them in a small album.  In addition to the picture, we record Hannah's weight and height, as well as some memorable moments from the past month.  Since we don't go to the doctor each month, I need to weigh Hannah myself in order to record her stats.  Our bathroom scale cannot measure such a light person, so we had to come up with another strategy besides sitting Hannah on our scale.  Another point to mention about a baby's weight and our scale, is that the doctor measures the baby's weight in pounds and ounces, while the scale measures by two tenths of a pound, in decimals.  From this scenario, I ended up coming up with several ways math skills are used to calculate Hannah's weight.  Below, I have grouped some questions by skill.  In the document on my Worksheets/Solutions page, there is a multi-step math problem incorporating the categories below.  Different groupings of these questions (or different numbers) could be used for different ages/grades or to allow for differentiation for different abilities in the classroom.

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Logic/Problem-Solving

• I wanted to be able to weigh Hannah in between doctor's appointments, but did not have a scale that could measure such a light person.
• How could I use a regular adult bathroom scale to measure Hannah's weight?

Conversions

• At the doctor's office, the nurse measures Hannah in pounds and ounces (example: Hannah weighed 6 pounds, 12 ounces when she was born).  However, my bathroom scale measures in pounds, with decimals that go up by two tenths (0.2).
• How could I use the bathroom scale to measure in pounds and ounces?
• What is an important piece of information you need to know in order to be able to solve this problem?
• According to my scale, I weigh 139.4 pounds.  Approximately, how many pounds and ounces is this?
• According to my scale, if I weigh myself while I am holding Hannah, we weigh 156.2 pounds total.  Approximately, how many pounds and ounces is this?

Subtraction with REGROUPING

(previously referred to as "borrowing")

• Using the decimal numbers given by the scale, how much does Hannah weigh?
• Using the conversions above, approximately how much does Hannah weight in pounds and ounces?
• Are the two answers above equivalent?  Why or why not?
• Check out THIS VIDEO for a tutorial on regrouping, in the base-10 number system, as well as with pounds & ounces, feet & inches, and with mixed numbers

**You can find an editable/printable version (using Word) of the above questions, along with solutions, on my Worksheets/Solutions page.

Age/Grade Guidelines:

In Massachusetts, the Common Core State Standards have been adopted.  Subtraction with regrouping is introduced in second grade (CCSS.MATH.CONTENT.2.NBT.B.7), and an algorithm for this is solidified by the end of fourth grade (CCSS.MATH.CONTENT.3.NBT.A.2, CCSS.MATH.CONTENT.4.NBT.B.4).  The skills necessary to complete the conversions in this scenario are introduced in fourth grade (fraction/decimal equivalence [CCSS.MATH.CONTENT.4.NF.C.6], multiplication with fractions [CCSS.MATH.CONTENT.4.NF.B.4]) and solidified during elementary school.  
The multi-step math problem on the Worksheets/Solutions page uses skills learned in elementary school; however, seeing as these skills need to be synchronized to reason about and calculate solutions, the problem (as written) would be appropriate for a challenging upper elementary, or middle school assignment.  As previously mentioned, different groupings of these questions (or different numbers) could be used for different ages/grades or to allow for differentiation for different abilities in the classroom.