Lesson 2 of 11
The number outside meets every term inside
Show on a big screenA school kit costs a ₹20 notebook plus a ₹5 pen. What do 8 kits cost?
Step 1 of 5
- 8 × (20 + 5). Two ways to one bill.
- Finish it: 8 × 25 = 200.
- Or, 8 × 20 = 160.
- And 8 × 5 = 40.
- 160 + 40 = 200 too.
The number outside meets every term inside
8 kits cost ₹200. You can add the prices first, or multiply each price by 8.
Each part of a sum is a term. In 20 + 5, the terms are 20 and 5.
Distributive property — multiply a sum by multiplying each part, then adding.
Rule: the number outside multiplies every term inside the bracket. Then the results add. In letters, a(b + c) = ab + ac. Here a, b and c stand for any numbers. Writing ab + ac for a(b + c) is called expanding the bracket.
- 8 × (20 + 5) = 8 × 20 + 8 × 5 = 160 + 40 = 200
- 7 × (20 + 3) = 7 × 20 + 7 × 3 = 140 + 21 = 161
- 24 × (31 + 1) = 24 × 31 + 24 × 1 = 744 + 24 = 768
Tap what the 8 multiplies. Slide the pen price. Match the real bill.
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Try the lab to finish this lesson.