CBSE Class 2 · Mathematics
Decoration for Festival (Addition and Subtraction)
Official NCERT chapter from Joyful Mathematics (English) (book code bejm1). ExamMaster notes are original teaching at CBSE Class 2 depth.
This lesson follows the official chapter “Decoration for Festival (Addition and Subtraction)” in Joyful Mathematics (English). The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.
- CBSE Class 2
- Easy level
- 8 concepts
1A garland of 10 flowers is a ten-bundle
Ten flowers on one garland is 1 ten. Loose flowers are ones. The garland is a house, not a decoration only.
Count garlands as tens. Count loose flowers as ones.
Figure. Ten flowers on one garland are one ten-bundle. The garland is a house for ten ones, not only a decoration. A leftover flower stays a one until nine more join it.
How it works
- Count full garlandsEach is 1 ten.
- Count loose flowersOnes.
- Read both housesTens, then ones.
2Join garlands as tens and leftover flowers
2 garlands and 4 loose flowers is 24 flowers. Join tens with tens, ones with ones.
Do not count a garland as one flower.
Figure. 2 garlands and 4 loose flowers is 24 flowers. Join tens with tens and ones with ones. The leftover flowers are not a third house.
How it works
- Add the tensGarlands.
- Add the onesLoose flowers.
- Regroup if ones make tenA new garland.
3Add two-digit numbers with tens and ones
36 + 21 is 3 tens + 2 tens and 6 ones + 1 one. Houses first, then join.
Adding 36 + 21 as 57 by a guess is not the house method.
Figure. 36 + 21 is houses first: 3 tens plus 2 tens, and 6 ones plus 1 one. That is 5 tens and 7 ones, so 57. The plus sign is written after the houses are named.
How it works
- Add ones6 + 1 = 7.
- Add tens3 + 2 = 5 tens.
- Read 575 tens and 7 ones.
Join 36 and 21
36 flowers and 21 flowers. How many together?
- Ones6 + 1 = 7
- Tens30 + 20 = 50
- Total57
Pro tip. Houses first. Do not count a garland as one flower.
4Regroup ten ones as one ten
8 ones + 7 ones = 15 ones = 1 ten and 5 ones. That new ten joins the tens house.
Leaving 15 in the ones house is a house error.
Figure. 8 ones plus 7 ones is 15 ones. Ten of those ones become one new ten; five ones stay in the ones house. The bar is split at 10 of 15, so the new ten is 10/15 of the bar.
How it works
- Add the ones8 + 7 = 15.
- Bundle ten of them1 ten, 5 ones.
- Carry the tenInto the tens house.
5Subtract with a borrow from the tens
42 − 17 needs a ten opened: 12 ones − 7 ones, then 3 tens − 1 ten. The opened ten is a borrow, not a new story.
Borrow only when ones are short. Do not borrow for show.
Figure. 42 − 17 needs a ten opened because 2 ones cannot give 7. Opening one ten turns 4 tens and 2 ones into 3 tens and 12 ones. Then 12 − 7 and 3 − 1. The opened ten is a borrow, not a new story.
How it works
- See if ones are short2 < 7, so yes.
- Open one ten12 ones, and tens lose 1.
- Subtract houses12 − 7, then 3 − 1.
42 take 17
42 flowers, 17 used on a door. How many remain?
- Ones short2 < 7
- Open a ten12 − 7 = 5 ones
- Tens3 − 1 = 2 tens
- Remain25
Pro tip. Join back to check: 25 + 17 = 42.
6A decoration story is join or take away
“More flowers on the door” is a join. “Gave a garland away” is a take-away. The story picks the action.
The mark waits for the story.
Figure. The decoration story picks the action. More flowers on the door is a join. Giving a garland away is a take-away. The marks + and − wait until the story has been named.
How it works
- Hear the storyAdded, or given away?
- Name the actionJoin, or take away.
- Then write the markLast.
7Estimate first by tens
36 + 21 is about 40 + 20 = 60. The estimate trains the houses. The exact join comes after.
An estimate you never check is not the answer.
Figure. On a 0-to-60 line, 36 sits at 36 and 21 at 21. Rounding to tens moves 36 to 40 and 21 to 20, so the estimate is 60. The exact join 57 comes after the houses have been trained by the estimate.
How it works
- Round to nearby tens36 near 40, 21 near 20.
- Join those tensAbout 60.
- Then do the exact houses57. The estimate was close.
8Check by the opposite action
A join is checked by taking the new group off. A take-away is checked by joining the leaving part back.
A failed check means the first action was wrong.
Figure. A join is checked by taking the new group off. 36 + 21 = 57 is checked by 57 − 21 = 36. The two arrows close a loop on the same three numbers.
How it works
- Name the first actionJoin, or take away.
- Do the oppositeTake off, or join back.
- Demand the startMust match.
8 ones + 7 ones should be written as
- 1 ten and 5 ones
- 15 ones left in ones
- 8 tens
Regroup ten ones as one ten.
Notes
- The official chapter title is “Decoration for Festival (Addition and Subtraction)”. Teach the school test for that title, not a contest shortcut.
- If a step needs a later class, stop. The next official chapter will pick it up.
Formulas
- Join tens with tens, ones with ones. Regroup 10 ones as 1 ten.
- Check: join \leftrightarrow take-away.
Recap
Hold these pegs from the official chapter “Decoration for Festival (Addition and Subtraction)”. The wording is ExamMaster’s teaching, not a textbook recap.
- A garland of 10 flowers is a ten-bundle
- Ten flowers on one garland is 1 ten. Loose flowers are ones. The garland is a house, not a decoration only.
- Join garlands as tens and leftover flowers
- 2 garlands and 4 loose flowers is 24 flowers.
- Add two-digit numbers with tens and ones
- 36 + 21 is 3 tens + 2 tens and 6 ones + 1 one.
- Regroup ten ones as one ten
- 8 ones + 7 ones = 15 ones = 1 ten and 5 ones.
- Subtract with a borrow from the tens
- 42 − 17 needs a ten opened: 12 ones − 7 ones, then 3 tens − 1 ten.
- A decoration story is join or take away
- “More flowers on the door” is a join. “Gave a garland away” is a take-away. The story picks the action.
Practise Decoration for Festival (Addition and Subtraction)
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- A 4-question practice set that ends the chapter
- 1 quick check with worked explanations
- Timed mocks scored with the real marking scheme
- Readiness tracked per topic, kept on your device