Finding the Unknown Number (in Addition) — Let's Practice!

Finding the Unknown Number (in Addition) — Let's Practice! exercise

• How many toys did Imani buy?

  Hints

  Remember, an equation looks like this: part + part = whole.

  To work out the missing part, think about how many more you need to add to 9 to reach 12.

  Look at this example: Imani has 10 sweets. They get more and now they have 14 sweets. How many did they get?

  The equation is: the part we know + the part we don't know = the whole we know.

  So

  10 + ? = 14

  Count on from 10 to reach 14. 10, 11, 12, 13, 14. We counted on 4 more, so 10 + 4 = 14.

  Solution

  Imani started with 9 toys and ended up with 12 in total, so the equation is 9 + ? = 12.

  To find the missing part, count on from 9 to 12. 9, 10, 11, 12. We counted on 3 so this is the missing part.

  9 + 3 = 12

  The equation 3 + 9 = 12 would also have been correct.

• Which numbers are missing?

  Hints

  Remember, to find the part we don't know, we count up from the part we do know until we reach the whole.

  Look at this example: 7 + ? = 14.

  We start at the part we know (7) and count up to the whole (14).

  7, 8, 9, 10, 11, 12, 13, 14. We counted on 7, so the missing part is 7.

  7 + 7 = 14

  Solution

  7 + 3 = 10 (7, 8, 9, 10)

  3 + 6 = 9 (3, 4, 5, 6, 7, 8, 9)

  8 + 7 = 15 (8, 9, 10, 11, 12, 13, 14, 15)

• What is the missing part?

  Hints

  Count up from the part you know until you reach the whole.

  Look at this example: 8 + ? = 14.

  We start at 8, and count up until we reach 14.

  8, 9, 10, 11, 12, 13, 14. The missing part is 6.

  8 + 6 = 14

  Solution

  5 + 6 = 11

  3 + 7 = 10

  9 + 4 = 13

  To find the missing numbers, we started at the part we knew and counted up until we reached the whole.

• How many flowers did Imani plant?

  Hints

  Remember, to create an equation, use the numbers you know. We know Mr. Squeaks planted 8 flowers. What else do we know?

  Look at the story. What is the whole? How many flowers did they plant together?

  An equation looks like this: part + part = whole

  To find the missing part, start at the part we know and count up to reach the whole.

  Solution

  Imani planted 5 flowers.

  The equation is: 8 + 5 = 13.

  We count up from one part (8) to the whole (13) to find the missing part.

  8, 9, 10, 11, 12, 13. The missing number is 5.

• How many more nails did Mr. Squeaks find?

  Hints

  Mr. Squeaks started with 5 nails and finished with 10. Count up from 5 to 10 to find the missing part.

  5, 6, 7, 8, 9, 10. How many numbers did we count up?

  Solution

  Mr. Squeaks found 5 nails in the box.

  Count on from 5 to 10: 5, 6, 7, 8, 9, 10. We counted 5 numbers, so 5 is the missing part.

  5 + 5 = 10.

• The vegetable patch.

  Hints

  Start with the tomato plants.

  Remember, to create an equation, use the numbers you know. We know Imani planted 4 tomatoes. What else do we know?

  Look at the story. What is the whole? How many tomatoes did they plant together?

  An equation looks like this: part + part = whole

  To find the missing part, start at the part we know (4) and count up to reach the whole (13).

  Repeat these steps for the bean plants.

  Solution

  Tomato plants

  • 4 + ? = 13
  • The missing part is 9.
  • Count on from 4 to 13. 4, 5, 6, 7, 8, 9, 10, 11, 12, 13. We counted 9 numbers, so 9 is the missing part.
  • 4 + 9 = 13

  Bean plants

  • 7 + ? = 11
  • The missing part is 4.
  • Count on from 7 to 11. 7, 8, 9, 10, 11. We counted on 4 numbers, so 4 is the missing part.
  • 7 + 4 = 11