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Lesson · Grade 4 · Mathematics

Finding the Number in the Box

  • Grade 4
  • Mathematics
  • 1 min 16 s
  • British Columbia
  • BC4-MA-20

A box hides part of 15 counters in □ + 4 = 15: taking away the 4 we can see leaves 11, and 11 + 4 = 15 checks the answer. The box then turns up with subtraction, multiplication and division (15 − □ = 11, □ × 3 = 12, □ ÷ 2 = 6), and each one is worked out, checked with a green tick and summed up in a one-line recap.

Concept: Finding the unknown number in a one-step equation

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In one sentence

The question this lesson answers

What number is hiding in the box?

Some number plus 4 makes 15.

Transcript

What the lesson says

What number is hiding in the box?

Some number plus 4 makes 15.

To find it, undo the plus 4 by taking 4 away from 15.

15 take away 4 leaves 11.

So the number in the box is 11.

Check: 11 plus 4 makes 15, so 11 is right.

A box can also hide when we subtract, multiply or divide.

Here, 15 take away the box leaves 11.

So the box is 15 minus 11, which is 4.

Check: 15 minus 4 is 11.

To undo times 3, divide: 12 divided by 3 is 4.

Check: 4 times 3 is 12.

To undo divided by 2, multiply: 6 times 2 is 12.

Check: 12 divided by 2 is 6.

Find the box from the numbers you know, then put it back in to check.

Curriculum

Where this fits

British Columbia, Grade 4

Mathematics, Patterns and algebra: one-step equations with an unknown number, using all operationsBC4-MA-20

Previous: From a pattern to a table of values

The outcomes and strands follow the British Columbia curriculum.

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