Represent the inverse relationship between addition and subtraction | Exit Quiz | Oak National Academy

Aisha picks up 4 beads. First, she picks up 3 white beads. Then, she picks up 1 red bead. She represents this with this equation 3 + 1 = 4 What subtraction equation would she write to undo this?

(a)  

Answer explanation

Great! The equation would be 4 − 1 = 3 because she starts the story with 3 beads and adds 1 more, so to undo the change, she must subtract 1 from the whole.

What amount will make this representation correct? What number is missing from the number line?

(a)  

Answer explanation

Well done! The missing number must be 4 because 8 − 4 = 8, so 4 + 4 = 8 To undo a change, we must add the same amount that was subtracted.

Alex collects some conkers. First, he puts 6 conkers in his pocket but then 5 conkers fall out. Now, he has 1 left. 6 − 5 = 1 Which equation would undo this change?

• 5 + 1 = 6

• 1 + 5 = 6

• 6 − 1 = 5

Answer explanation

Well done! 1 + 5 = 6 would undo this change. Because 5 conkers were lost (subtracted), these must be added on to undo the change. We could say: First, Alex had 1 conker. Then, he collected 5 more. Now, he has 6 conkers.

Which pair of equations are being shown in this picture?

• 5 − 4 = 1 1 + 4 = 5

• 4 − 3 = 1 1 + 3 = 4

• 4 − 1 = 3 3 + 1 = 4

Answer explanation

Great! At the start of the story there were 4 counters. Then, 1 was subtracted. So, there were 3 counters. Then, 1 counter was added. Now, there are 4 counters.

Aisha and Alex are telling their own 'First, then, now' stories for this picture. Who is correct?

• Aisha says, "First I had 3 cubes. Then Alex gave me 6 more. Now I have 9 cubes."

• Alex says, "First I had 9 cubes. Then I gave 6 to Aisha. Now I have 3 cubes."

• Both Alex and Aisha are correct.

Answer explanation

Excellent! Both children are correct. Alex has described the first part of the picture, which is a subtraction story 9 − 6 = 3 Whereas, Aisha has described the final part, which is the inverse 3 + 6 = 9 Both stories can been seen in this picture.

I created a picture to show a 'First, then, so, then, now' story. How much was added to the amount at the start of the story?

• 3 pounds

• 1 pound

• 4 pounds

Answer explanation

Well done! The second part of the story shows that 3 pounds are being subtracted from 4 pounds, 4 - 3 = 1 So 3 pounds must have been added in the first part of the story, 1 + 3 = 1