5 brainy tricks to make your kids maths geniuses

These clever hacks will help your kids estimate the number of jelly beans in a jar, leaves on a tree, and more.

By Rachel Ng
Published 12 Sept 2022, 13:29 BST
Girl with Jellybeans - Brainy Tricks
Young girl looking at bowl of colorful jellybeans. British Virgin Islands
Photograph by Anya Brewley Schultheiss, Getty Images

One afternoon, Lori Anderson and her 7-year-old, Lindsey, spotted a small maple tree in La Mirada, California. Anderson asked her daughter how many leaves she thought were on the tree. Lindsey’s guess? “Probably a million.”

Lindsey can grasp the concept of large numbers, and she knows that a million is a lot of leaves. She doesn’t yet have the tools to make a true estimation on her own, but scientists say this is a crucial skill for children to learn.

Estimation is more than just a guess—it’s a conclusion that comes from a methodical thought process using data and facts. “We don’t just look at something and estimate. We discuss with other people how to approach it or how to look at proportions,” says Rebecca Mannis, a learning specialist who’s focused on neuroscience and education. “We also have to be able to imagine how details fit together.”

Why children need to be expert estimators

Kids who are expert estimators exercise brain skills like critical thinking, imagination, visualisation, organisation, and communication. For example, when estimating how many cookies it will take to fill a cookie jar, a child might discuss with their parents whether those cookies are bite-size or palm-size, visualise how many of those cookies will fit in each layer, imagine the space in the jar in 3D, and think critically about how those calculations add up.

Making estimations is also a great way to introduce math concepts like counting and multiplication—even to toddlers. In fact, a 2013 study by the University of Missouri found that preschool children who were unable to estimate the number of objects in a group were more likely to experience difficulties in understanding math at a later age.

As adults, they’ll need these skills to shop on a budget or buy enough paint for a wall. Researchers say that parents can help children develop estimation skills by helping them understand how numbers relate to quantities in real life. That’s because when children learn using tangible materials, they can explore and reinforce estimation through trial and error. And rather than arriving at the “right” answer, the goal of learning to estimate is to go through the thought process. “It helps them learn how to approach thinking about information,” Mannis says.

Here are five estimation hacks to help kick-start your child’s critical thinking and estimation skills.

ESTIMATION: How many leaves are on that tree?
BRAIN SKILLS: Counting and multiplication

When you ask a kid how many leaves are on a tree, you’ll get an answer anywhere from a hundred to a bazillion. Real forestry researchers sometimes measure the area beneath the crown of a tree or count the fallen leaves and use that number to estimate the percentage of the remaining leaves. You can help your children make their own estimation by starting small.

  • Help your kids count the number of leaves on one twig on the tree.
  • Have them find a branch and ask your kids to count how many twigs it has.
  • Count the number of branches on the tree.
  • Take the number of leaves on a twig and multiply that by the number of twigs on a branch. Then multiply that number by the branches on a tree.

ESTIMATION: How many jelly beans are in that jar?
BRAIN SKILLS: Division, counting, and multiplication

Help your children win a counting contest using one of two ways to make this estimation.

  • Weigh the empty jelly bean jar, then weigh the jar full of beans. Finally, weigh one single jelly bean.
  • Take the difference in the weight and divide it by the weight of a single jelly bean.
  • If you don’t have a scale, have your kids look at the underside of the jar and count the number of jelly beans on the bottom.
  • Next, have them count the number of layers of jelly beans in the jar.
  • Multiply those two numbers to get your estimation. If the jar isn’t a perfect cylinder, add a few more jelly beans for a more accurate count.

ESTIMATION: How long is that fence?
BRAIN SKILLS: Visualisation and counting

Your kids don’t need a ruler or measuring tape to make a quick estimation of length, just an understanding of how long they are.

  • Measure the length of your child’s hand from their thumb to their pinkie when their fingers are spread out. Next, measure their feet from the heel to the toe. Finally, get the measurement from their elbow to the tip of their middle finger.
  • Use their hand span to estimate the width of a door, the foot to estimate the size of a room, and the elbow to estimate the length of a fence.

ESTIMATION: What time will the sun set?

A useful hack when camping or out on a hike, all you need are adult hands—and a kid’s help—to figure out how quick the sun will set for the day.

  • On a clear afternoon, search the horizon for a spot unblocked by trees or buildings.
  • Hold out your arm with your palm turned toward your face with your pinkie resting on the horizon line. Enlist your child to help your arm stay steady.
  • Keeping your thumbs tucked in, stack one hand above another until they reach the sun.
  • If it takes more than two hands, your kid should help you move your bottom hand to the top while you hold the other hand steady.
  • Each adult hand represents an hour, and each finger is about 15 minutes. So, if it takes three hand measurements and two fingers, that means the sun will set in roughly three hours and 30 minutes. (If your child has bigger hands, they can try this trick themselves.)

ESTIMATION: How tall is that tree?

  • Choose a tree that’s on flat ground. (This won’t work in a hilly area!)
  • Find a stick that’s the length of your child’s arm.
  • Have them stretch out their arm in front of them and hold the stick straight up to create a 90-degree angle facing the tree.
  • Walk backward until the top of the stick is aligned with the peak of the tree.
  • Have kids walk heel-to-toe toward the tree until they are face-to-face with the trunk. The number of steps is the approximate height of the tree in feet.

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