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Classroom activity Grade 2 Math

Bramblewick's Drip Cards: A Grade 2 Make-100 Matching Game

Ten cards show the cups a leaky fixture wastes in a day, and groups hunt for the five pairs that add to exactly 100 cups, one full jug.

Objectives

  1. Students will find the number that makes 100 when added to a given two-digit number.
  2. Students will add and subtract two-digit numbers to check a partner's pair.
  3. Students will count by hundreds to total five pairs.

Vocabulary

Key words: pair, total, leak, drip, jug

Teacher overview

Groups of three or four play a memory-style matching game with ten number cards, each card showing the cups of water that one leaky fixture wastes in a single day at a school in the town of Bramblewick. Two cards match when the numbers add to exactly 100 cups, which is one full jug, so each match shows that two small daily drips together fill a container students can picture. The misconception this game exposes is the tens-only complement, in which a student pairs 38 with 72 because thirty and seventy make a hundred and the ones are ignored. Require every group to say the full sum aloud before keeping a pair, which forces the ones digits into the check.

Activity Directions

  1. Before class, print one card set per group and cut the ten cards apart. Each set holds the numbers 15, 85, 24, 76, 38, 62, 45, 55, 9, and 91.
  2. Seat students in groups of three or four. Tell them that each card is one leaky fixture at a school in the town of Bramblewick, and that the number is the cups that fixture wastes in one day. Show a labeled 100 cup jug drawn on the board so the target is a picture, not just a number.
  3. Have each group shuffle its ten cards and lay them face down in two rows of five.
  4. Play in turns. A student turns over two cards and says the sum aloud. If the sum is exactly 100 cups, the student keeps the pair and takes another turn. If it is not 100, the cards go back face down and play passes to the left.
  5. Require the group to agree on the sum before any pair is kept. If the group disagrees, they settle it by counting up from the smaller number on a hundred chart.
  6. The round ends when all five pairs have been found, or after 15 minutes, whichever comes first. Groups that finish early shuffle and play again, this time racing their own first-round time.
  7. Hand out the recording page and give students 8 minutes to answer the six questions on their own.
  8. Close with a two-question debrief: ask how a student decided which card completed 100 with the 38 card, and ask what the five pairs together say about ten small drips left unfixed for a day.
Bramblewick's Drip Cards: A Grade 2 Make-100 Matching Game — Grade 2 Math
Name: ____________________________ Date: ______________

Student Handout

Suppose you play the drip card game at the school in the town of Bramblewick. The ten cards show 15, 85, 24, 76, 38, 62, 45, 55, 9, and 91.

  1. One card shows 15 cups. Its partner makes 100 cups. What number is on the partner card?
  2. A pair shows 24 cups and 76 cups. How many cups is that in all?
  3. One card shows 38 cups. What number makes 100 cups with it?
  4. One card shows 91 cups and one card shows 9 cups. How many more cups does the 91 card show?
  5. Your group has found 3 pairs. Each pair makes 100 cups. How many cups is that in all?
  6. All 5 pairs make 100 cups each. How many cups do all ten cards show in all?

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: 85 cups. Count up from 15 to 100, or subtract: 100 - 15 = 85.
  2. Answer: 100 cups. Add the pair: 24 + 76 = 100.
  3. Answer: 62 cups. Subtract to find the missing part: 100 - 38 = 62. A student who answers 72 has matched only the tens.
  4. Answer: 82 cups. This is a compare problem: 91 - 9 = 82.
  5. Answer: 300 cups. Count by hundreds for the three pairs: 100, 200, 300.
  6. Answer: 500 cups. Count by hundreds for the five pairs: 100, 200, 300, 400, 500.

Differentiation

Support

Give these groups a hundred chart and only six cards, using the pairs 15 with 85, 24 with 76, and 45 with 55, so two of the three pairs use friendly multiples of five. Let students lay the cards face up for the first round so the game becomes a search rather than a memory task.

Extension

Ask these students to write two new cards that pair to 100 and are not already in the set, then prove each pair with a number sentence. A further challenge is to find three cards in the set that add to more than 200 cups and to show the addition.

ELL supports

Bring a marked one-gallon jug or a stack of paper cups to make the word "cups" concrete before the game begins. Post the sentence frame "___ and ___ make 100 cups," and have students say it each time they keep a pair, which gives every player the same repeated phrase.

Extensions

Give each group a fresh set in which the target is 50 cups instead of 100 cups and ask them to write the ten card numbers themselves before playing. Building the set requires the same reasoning as the game, and comparing the two targets prepares students to think about the missing part in a subtraction sentence.