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FETCH!: Birthday Calculator Math

What's The Point

Using a calculator to solve a repeat addition problem and then solving the same problem with multiplication is a great way to introduce kids to the relationship between addition and multiplication. When the problem involves groups of weeks and months, kids learn about the calendar as well.

Related Game

FETCH! Fone – Explore the concepts of time and money.

This Activity Will Help Your Child

  • Understand the concept of days, weeks, and months
  • Practice addition and early multiplication

Book Suggestions

  • 365 Penguins
    by Jean-Luc Fromental
  • A Child’s Calendar
    by John Updike


  • Calculator
  • Stop watch or watch with a second hand

How Do I Do It?

  1. Ruff Ruffman lost his calculator. He bought a new one, and made up some calculator games to test it out. Ask your child if she'd like to play Ruff's calculator games. She may think she's just having fun with a calculator, but she'll really be learning about weeks, months and years.
  2. For the first game, ask your child to use the calculator to figure out how many months old she'll be on her next birthday. Explain to her that there are 12 months in a year. So to find out her age in months she'll have to add as many 12s as she is years. For example, if she'll be 7 on her next birthday she'll have to add 12 seven times: 12 + 12 + 12 +12 + 12 + 12 + 12 = 84. She'll be 84 months old! Show your child that multiplying 7 x 12 on the calculator is another way to find out how many months there are in 7 groups of 12.
  3. Next, ask your child to calculate how many weeks old she'll be on her next birthday. There are 52 weeks in a year, so she'll have to add 52 a total of 7 times: 52 + 52 + 52 + 52 + 52 + 52 + 52 = 364. She'll be 364 weeks old! Multiplying 52 x 7 is another, quicker, way to get to the same answer.
  4. If she got a year older every day, ask her to figure out how old she would be in a week. Explain that there are seven days in a week so at the end of a week she would be seven years older!
  5. Suggest that your child try out some of these games on other members of the family, including her parents!

Take It Further

Another fun calculator activity that combines math and science is measuring your heartbeat. Show your child the best place to feel her pulse (under her chin or at the wrist). Use a stopwatch or the second hand of a watch to measure the number of beats in 10 seconds. Either add this number together 6 times or multiply it by 6 to get how many beats per minute.

Ask your child what he thinks will happen to her heartbeat after she jumps up and down for a minute. Try it and find out.