Math in Our World: A Soapy Situation

It’s important to wash your hands to keep them clean.

To help wash her hands for long enough to get all the germs off, Kim counts for 20 seconds. That lets her know that she spent enough time using soap and water.

Sometimes Kim counts to 20.

Sometimes she counts to 15, and then she counts to 5.

Sometimes she counts to 12, and then she counts to 8.

Sometimes she counts to 5 four times in a row.

Rubbing soapy hands together at the sink.
  1. Use numbers, math words, objects, or pictures to show the ways Kim counts.
  2. What do you notice? What do you wonder?
  3. What math questions can you ask about the situation? Answer the questions that you can!
  • Can you think of other ways Kim can count? You can use any two numbers that make 20!
  • If you’re stuck, use a number rack. How can you move the beads on the rack to make 20 in different ways? If helpful, you can also use the Number Rack app.
  • Think about counting to 10 and then counting 10 more. What happens if you change the first number to 11? How does that change the other number you count to?
  • Feeling creative? Try skip-counting! You can count by 2s, 5s, or 10s while you wash your hands. Can you say the first 20 numbers in your skip-counting pattern?
  • Can you come up with a different way to count each time you wash your hands?
  • The next time you wash your hands, show someone else how you’re counting. Use numbers and math words to explain your thinking. Ask them if they have any questions about how you’re counting.

Think of other ways to use math while you wash your hands. You might count backward or count by 2, 5s, or 10s. Remember, you’ll need to count 20 numbers to spend the right amount of time. Maybe you know a math song that takes about 20 seconds. We’d love to hear your ideas!