What is Left?

S0-SA2-0197

Grade Level:

Pre-School

Geometry, Robotics, Computing, Direction

Definition

What is it?

In mathematics, 'Left' refers to the amount remaining after something has been used, taken away, or consumed. It is the result of a subtraction operation, telling us how much is still there from an original quantity.

Simple Example

Quick Example

Imagine you have 10 ladoos in a box. If your friend eats 3 ladoos, the number of ladoos 'left' in the box is 7. You started with 10, and 3 were taken away.

Worked Example

Step-by-Step

Problem: A chai-wala made 25 cups of chai. If he sold 18 cups, how many cups of chai are left?

Step 1: Identify the starting quantity. The chai-wala started with 25 cups.
---Step 2: Identify the quantity that was used or taken away. He sold 18 cups.
---Step 3: To find what is 'left', we subtract the used quantity from the starting quantity.
---Step 4: Calculation: 25 - 18
---Step 5: Perform the subtraction. 25 - 18 = 7
---Answer: There are 7 cups of chai left.

Why It Matters

Understanding 'left' is crucial for daily calculations and problem-solving. In Robotics, it helps robots know how much battery is 'left' or how much distance is 'left' to cover. In Computing, it's used to calculate remaining memory or data. Engineers and scientists constantly use this concept.

Common Mistakes

MISTAKE: Adding instead of subtracting when trying to find what's left. For example, 'I had 5 apples, I bought 3 more, how many are left?' and adding 5+3. | CORRECTION: 'Left' almost always implies subtraction. If something is taken away or used, you subtract.

MISTAKE: Subtracting the original amount from the amount taken away, especially if the 'taken away' number is larger (e.g., 5 - 10). | CORRECTION: Always subtract the smaller (used/taken away) quantity from the larger (original) quantity to find what is left.

MISTAKE: Forgetting to account for all items removed or used. For example, if two people take items, only subtracting for one. | CORRECTION: Ensure you subtract the total amount that has been used or removed from the original quantity.

Practice Questions

Try It Yourself

QUESTION: You have 50 rupees. If you buy a packet of biscuits for 15 rupees, how much money is left? | ANSWER: 35 rupees

QUESTION: A bus has 45 seats. If 28 passengers are already seated, how many seats are left empty? | ANSWER: 17 seats

QUESTION: A farmer harvested 120 kg of mangoes. He sold 75 kg in the morning and gave 10 kg to his family. How many kg of mangoes are left? | ANSWER: 35 kg

MCQ

Quick Quiz

If a mobile phone battery starts at 100% and uses 35% by lunchtime, what percentage is left?

35%

65%

135%

75%

The Correct Answer Is:

To find what is left, we subtract the used percentage from the starting percentage: 100% - 35% = 65%. Options A, C, and D are incorrect calculations.

Real World Connection

In the Real World

When you check your mobile data usage, your phone tells you how many GBs of data are 'left' from your monthly plan. Similarly, when you buy groceries, the shopkeeper calculates how much change is 'left' for you after you pay.

Key Vocabulary

Key Terms

SUBTRACTION: The process of taking one number or quantity away from another. | REMAINDER: The amount left over after a calculation. | QUANTITY: An amount or number of something. | CONSUMED: Used up or eaten.

What's Next

What to Learn Next

Now that you understand 'What is Left?', you can explore 'Addition' and 'Subtraction' in more detail. These concepts are fundamental building blocks for all of mathematics, helping you solve more complex problems.