For parents
Subtraction to 10: take away and compare with blocks
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“How many are left?” and “How many more?” can lead to the same subtraction. But the objects tell two different stories. Use these short activities to explore both meanings of 5 − 2 = 3.
Set up two counting spaces
Gather up to 10 large, age-appropriate blocks and two sheets of paper. For comparisons, choose blocks of a similar size so that physical length does not distract from the number of objects. Start with five if counting to 10 is still challenging. There is no need for a timer: leave room for your child to move and point to each block.
How many are left? Show 5 − 2
Put five blocks on one sheet. Count them together, touching each once. Say, “We have five. We move two off the paper.” Let your child move exactly two away, then count only those still on the sheet: one, two, three. Write 5 − 2 = 3. Five is the starting amount, two is the amount removed and three is what remains. Check by putting the two back: 3 + 2 = 5.
How many more? Compare two rows
Make a top row of five blocks and a bottom row of two. Start the rows in the same place, with each bottom block directly below a top one. Two pairs match; three top blocks have no partner. Ask, “How many more blocks are in the top row?” The answer is three, so write 5 − 2 = 3 again. This time nothing moves away. You are finding the difference, not counting all seven blocks. NCETM describes this comparison meaning in its resource on subtraction as difference, linked below.
Play a car park game
The paper is a car park and the blocks are cars. Your child chooses between three and ten cars. Tell a story about some driving away; your child moves them onto the other sheet and works out how many remain. Swap roles. In a later round, build two car parks and ask which has more cars and how many more. Keep the questions separate: first a complete take-away round, then a comparison round.
Four problems with explained answers
6 − 2 = 4: start with six blocks, move two away and count the four left. 7 − 4 = 3: match rows of seven and four; three blocks in the longer row have no partner. 5 − 0 = 5: if no cars leave, the number stays the same. 4 − 4 = 0: if all four cars leave, the car park is empty. Offer one problem at a time and read the answer after your child has tried. Ask them to show their answer, as well as say it.
Common mix-ups and useful prompts
If your child counts the removed blocks, point to the car park and ask, “How many are still here?” When comparing, avoid asking “How many altogether?” at the same time: that is a different question. If two widely spaced blocks seem like a larger group, match the blocks in pairs again. In the take-away story, 5 − 2 cannot simply be swapped to 2 − 5: the starting group is five and the amount removed is two.
Finish with a story, then practise
Ask your child to invent a story for 5 − 2. If both meanings are comfortable, change the numbers while staying within 10. If it feels tiring, stop after one successful round. A parent can later choose the subtraction book in Otto Math on iPhone or iPad. The first five routes in each book are free; further routes require Otto Plus. The real-block activity works as a complete activity on its own.