Using a Third Thing

Compare two things that cannot be moved.

10 problems · about 11 minutes · 1.MD.A.1

What this lesson teaches

The child compares two objects that cannot be placed side by side, using a string as a go-between.

From earlier lessons. Loosen up before the new work.

7 problems

Review — Longer Than, Shorter Than: Why must you line up one end before comparing?
Answer Otherwise you cannot tell which is longer.
Why Lining up the ends is what makes the comparison fair.
Review — True or False to Twenty: Is 13 − 9 = 2 + 2 true?
Answer True. Both are 4.
Why Both sides come to 4.
Review — Missing Numbers to Twenty: 8 + ? = 12
Answer 4
Why 8 + 4 = 12.
Review — Take From Ten in Stories: 11 − 8 = ?
Answer 3
Why 11 − 8 = 2 + 1 = 3.
Review — Taking From Ten: 13 − 9 = ?
Answer 4
Why 13 − 9 = 1 + 3 = 4.
Review — Counting On or Making Ten?: 8 + 2 = ?
Answer 10
Why 8 + 2 = 10.
Review — Start With the Bigger One: 6 + 9 = ?
Answer 15
Why 9 + 6 = 10 + 5 = 15.

Straightforward practice. Get the method working first.

2 problems

A rope is shorter than a string. The string is shorter than a pole. Is the rope shorter than the pole?
Answer Yes.
Why Rope is under string, string is under pole, so rope is under pole.
Why use a string instead of moving the door?
Answer Because the door cannot be moved.
Why A string can go to the object when the object cannot come to you.

Mixed problems. Work out what kind of question it is before you start.

1 problem

The Bookcase: A shelf is longer than a string. The string is longer than a book. Is the shelf longer than the book?
Answer Yes, the shelf is longer.
Why If the shelf beats the string and the string beats the book, the shelf beats the book.