What is Making Twenty?

S0-SA1-1416

Grade Level:

Pre-School – Class 2

All domains without exception

Definition

What is it?

Making Twenty means finding different ways to combine numbers, usually by adding, to get the total sum of 20. It helps us understand number relationships and practice basic addition.

Simple Example

Quick Example

Imagine you have 15 cricket runs. How many more runs do you need to reach 20 runs? You need 5 more runs, because 15 + 5 = 20. This is one way of 'Making Twenty'.

Worked Example

Step-by-Step

Let's find one way to make 20 using two numbers.

STEP 1: Start with a number less than 20, for example, 12.
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STEP 2: We want to find out what number we need to add to 12 to reach 20.
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STEP 3: We can think: 12 + ? = 20.
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STEP 4: To find the missing number, we can subtract 12 from 20. So, 20 - 12 = 8.
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STEP 5: This means 12 + 8 = 20.

So, 12 and 8 are two numbers that 'Make Twenty'.

Why It Matters

Understanding how numbers combine to make a specific total is a foundational skill in mathematics. It's crucial for mental math and problem-solving in everyday life. This skill is used by shopkeepers calculating change, engineers designing structures, and even by financial analysts managing budgets.

Common Mistakes

MISTAKE: Only thinking of 10 + 10 as the only way to make 20. | CORRECTION: Remember there are many combinations, like 19 + 1, 15 + 5, 11 + 9, and even more with three or more numbers.

MISTAKE: Confusing making 20 with making other numbers like 10 or 100. | CORRECTION: Always check that your sum equals exactly 20, not any other number.

MISTAKE: Forgetting that subtraction can help find missing numbers when making 20 (e.g., if you have 7, what do you need to add to make 20? 20 - 7 = 13). | CORRECTION: Use subtraction as a tool to find the 'other half' needed to reach 20.

Practice Questions

Try It Yourself

QUESTION: If you have 8 rupees, how many more rupees do you need to have 20 rupees? | ANSWER: 12 rupees

QUESTION: My mom bought 13 laddoos. How many more laddoos does she need to have a total of 20 laddoos? | ANSWER: 7 laddoos

QUESTION: A bus has 6 passengers. At the next stop, 5 more passengers get on. How many more passengers are needed for the bus to have exactly 20 passengers? | ANSWER: 9 passengers (6 + 5 = 11, and 20 - 11 = 9)

MCQ

Quick Quiz

Which pair of numbers adds up to make 20?

7 and 10

12 and 8

15 and 4

11 and 11

The Correct Answer Is:

12 + 8 = 20, so this pair makes 20. Options A, C, and D add up to 17, 19, and 22 respectively, not 20.

Real World Connection

In the Real World

When a shopkeeper gives you change after you buy something, they are often 'making a total' in their mind. For instance, if an item costs 12 rupees and you give 20 rupees, the shopkeeper quickly calculates 20 - 12 = 8 rupees change. This is a practical application of 'Making Twenty'.

Key Vocabulary

Key Terms

ADDITION: The process of combining numbers to find a total sum | SUM: The total result obtained from adding two or more numbers | COMBINATION: Different ways numbers can be put together | MENTAL MATH: Doing calculations in your head without paper or calculator

What's Next

What to Learn Next

Now that you understand Making Twenty, you're ready to explore 'Making One Hundred'. This will help you work with larger numbers and strengthen your mental math skills even more, which is super useful for bigger calculations!