Laura Wolff
(Adapted from “Measurement Division” Activity 8.5, page 315, in Guiding Children’s Learning of Mathematics, Tenth edition, by Leonard M. Kennedy, Steve Tipps, and Art Johnson.
Content Areas: Math, repeated subtraction, division
Grade Level: 2-4
Materials Needed: small paper cups, large bag of almonds (or other small items)
Key Concepts: repeated subtraction
EALR”S:
· show understanding of whole number operations using manipulatives,
· recognize, create, and extend patterns of objects and numbers using a variety of materials such as beans, toothpicks, cubes, etc.
· define problems in familiar situations,
· interpret and compare information in familiar situations,
· identify the unknowns in familiar situations,
· reflect on and evaluate procedures and results in familiar situations,
· organize and clarify mathematical information in at least one way- reflecting, verbalizing, discussing, or writing
· express mathematical ideas to familiar people using everyday language
Goals: students work in pairs and explore real life math problems using small objects and containers and everyday language to model measurement division (repeated subtraction).
Objectives: Given a repeated subtraction scenario, students will work with partners using paper cups and small objects to find the solution to the problem. After an all class, teacher guided explanation of the problem, followed by further examples, students will be able to solve similar repeated subtraction scenarios, using their manipulatives, on their own.
Procedures: Students will be sitting at their desks or on the floor in pairs, with 9 paper cups and 40 almonds per pair. “For math today I am going to be telling you a story about a guy named Philip and a party that he is getting ready. I want you and your partner to use the paper cups and almonds to figure out how Philip should plan for his party.” “ Is everyone ready for the first part of the story?” “Get ready to listen and I will also write some numbers on the board.” “Philip started out preparing nut cups for a party. He had 35 almonds and put 5 almonds into each cup. How many cups did he use?” (Teacher writes “35 almonds” and “5 almonds in each cup” on the board, and “How many cups?”) “You and your partner need to count out 35 almonds and set the rest to the side.” “Find out how many cups Philip filled by putting 5 almonds in each cup.” Walk around and observe children as they work, give clues to any who need assistance. When all children are finished, write 35, 5, and 7 on the board. Then ask, “What do each of these numbers up here that I have written on the board mean? Raise your hand if you have an idea.” (35 is the total number of almonds, 5 is the number of almonds in each cup, and 7 is the total number of cups.) “ We started with 35 almonds in all. Then we started putting 5 almonds in each cup. If we subtract 5 from 35, how many almonds do we have left?” (30) “I am going to keep subtracting 5 from 35 and I want you to keep track on your fingers how many times I take 5 away until we get to 0.” “Here we go, I have 35 almonds and I take away 5, how many do I have left?” (30) “ So that’s 1 time that I’ve take away 5” (teacher shows students to hold up one on their fingers.) “30 take away 5 is ____?” (25) Students show two on their fingers. Keep doing this until you get to 0, and the students have seven on their fingers. “How many times did I subtract 5 from 35? (7) “How does this relateto what our exercise that we just did with Philip and his party cups?” (Students should make the connection between their 7 fingers and the 7 party cups, with 5 almonds in them each.)
Time permitting, repeat exercise with other quantities and groupings of almonds. Discuss each situation as it is completed to help children realize that each time they separate a set of almonds into groups of a known size, they determine the number of cups into which the almonds are placed.
Assessment: Students will be given a worksheet with 3 problems similar to ones covered in this activity. They will do their own work and will use their paper cups and small objects to solve the problems. Teacher will walk around and observe students working to check for understanding and to offer assistance if necessary.