NCERT Exemplar Solutions
Class 6 - Mathematics - Unit 7: Algebra - Multiple Choice Questions

Question 11

1. In algebra we often use letters like \(x\), \(y\) or \(a\).

2. These letters act like placeholders for numbers we don’t know yet.

3. Example: \(x + 5 = 12\)

4. Here, \(x\) is the number we are trying to find (an unknown).

5. We can figure it out step by step:

   \(x + 5 = 12\)

   \(x = 12 - 5\)

   \(x = 7\)

6. So, letters in algebra usually stand for unknown quantities. That matches option B.

Why the other options are not the best here:

• A. known quantities: If a number is already known, we can just write the number itself. We don’t need a letter for it in basic problems.

• C. fixed numbers: Sometimes a letter can represent a fixed number (for example, \(\pi\)), but in school algebra questions like this, letters mainly show unknowns we need to find.

• D. none of these: Not correct, because option B fits well.