Mathematics · Class 1

Active learning ideas

Adding and Subtracting Decimals

Active learning builds fluency in decimal operations by making place value visible through hands-on work. When students physically align numbers or solve real shopping problems, they see why 2.50 rupees is not the same as 2.5 rupees, strengthening their understanding beyond abstract rules.

• CBSE Learning Outcomes
• NCERT: Class 7, Chapter 2, Fractions and Decimals

• 25–45 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Placemat Activity
• 30 min · Pairs

Pair Matching: Decimal Alignment Puzzles

Prepare cards with decimals split into place value components. Pairs match and align them on a grid mat to form complete addends or minuends, then compute the result. They verify by checking with a calculator and explain their alignment to each other.

Explain the importance of aligning decimal points during addition and subtraction.

Facilitation Tip

During Pair Matching, provide laminated decimal strips so students can slide numbers to check alignment before writing.

What to look for

Present students with three addition problems (e.g., 5.6 + 2.3, 10.15 + 4.05, 7.89 + 1.2) and three subtraction problems (e.g., 9.8 - 3.5, 15.75 - 6.25, 12.34 - 5.67). Ask students to solve them on a worksheet, showing their work with aligned decimal points.

• Understand
• Analyze
• Evaluate
• Self-Awareness
• Relationship Skills

Activity 02

• Placemat Activity
• 45 min · Small Groups

Small Group: Market Budget Challenge

Provide price lists of fruits and vegetables in decimals. Groups plan a budget under Rs 100, adding costs and subtracting from total money. They present their shopping list, justifying alignments and totals to the class.

Analyze common errors made when adding or subtracting decimals.

Facilitation Tip

In the Market Budget Challenge, give each group fake currency notes and price tags in paise to encourage careful addition and subtraction.

What to look for

Give students a card with the following prompt: 'Rohan bought a notebook for ₹45.50 and a pen for ₹15.25. Calculate the total cost. If he paid with a ₹100 note, how much change will he receive? Show your calculations clearly.'

• Understand
• Analyze
• Evaluate
• Self-Awareness
• Relationship Skills

Activity 03

• Placemat Activity
• 35 min · Whole Class

Whole Class: Error Hunt Relay

Display problems with deliberate decimal errors on the board. Teams send one student at a time to identify and correct one error, aligning points correctly before tagging the next. Discuss solutions as a class at the end.

Design a budget scenario that requires decimal addition and subtraction.

Facilitation Tip

For the Error Hunt Relay, prepare strips with one error each so students focus on identifying and correcting decimal misalignment quickly.

What to look for

Ask students: 'Imagine you are helping your mother at home. She asks you to measure 2.5 litres of water and then pour out 1.25 litres. How would you explain the steps to find out how much water is left? What is the most important step in this calculation?'

• Understand
• Analyze
• Evaluate
• Self-Awareness
• Relationship Skills

Activity 04

• Placemat Activity
• 25 min · Individual

Individual: Decimal Number Line Race

Students mark decimals on personal number lines, then add or subtract by jumping intervals. They race to complete a set of five problems accurately, self-checking with answer keys provided.

Explain the importance of aligning decimal points during addition and subtraction.

Facilitation Tip

With the Decimal Number Line Race, have students use movable decimal cards on a number line to visualize jumps of tenths and hundredths.

What to look for

Present students with three addition problems (e.g., 5.6 + 2.3, 10.15 + 4.05, 7.89 + 1.2) and three subtraction problems (e.g., 9.8 - 3.5, 15.75 - 6.25, 12.34 - 5.67). Ask students to solve them on a worksheet, showing their work with aligned decimal points.

• Understand
• Analyze
• Evaluate
• Self-Awareness
• Relationship Skills

A few notes on teaching this unit

Teachers should begin with concrete models like base-10 blocks adapted for decimals or decimal grids to show that each square represents hundredths. Avoid rushing to the algorithm; let students discover rules through guided questions. Research shows that students who explain their steps to peers internalize decimal operations more deeply than those who only practice silently.

Students will confidently line up decimal points, justify trailing zeros, and explain borrowing steps with concrete materials. They should connect calculations to everyday contexts like rupees and paise and describe their process clearly to peers.

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Watch Out for These Misconceptions

• During Pair Matching, watch for students who ignore decimal points and treat numbers as whole numbers.

  Ask them to lay out the decimal strips and count the columns together, pointing out how misalignment changes the value from 1.2 to 12.0. Have peers demonstrate the correct stacking.

• During Market Budget Challenge, watch for students who drop trailing zeros in prices like ₹2.5 as ₹2.50.

  Give them decimal grids to shade fully and ask them to compare ₹2.50 with ₹2.5 on the grid. Discuss how the extra zero shows the paise place is filled.

• During Error Hunt Relay, watch for students who borrow across the decimal point as if it were a whole number.

  Hand them base-10 blocks adapted for decimals and ask them to model the borrowing step-by-step, noting that each borrowed unit stays within its decimal place.

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Methods used in this brief

• Placemat Activity