Chapter 3

The World of Numbers

CBSE Class 9

Mathematics Solutions

Question:

Explain, using a real-world example of debt, why subtracting a negative number is the same as adding a positive number (e.g., 10 - (-5) = 15). [Page No. 46]

Answer: Verified

Imagine you have ₹ 10 in your pocket, and you owe a friend ₹ 5, which is a debt of ₹ 5.

If your friend forgives this debt, you no longer have to pay ₹ 5.

So, your money increases by ₹ 5, and your total becomes ₹ 10 + ₹ 5 = ₹ 15.

This shows that subtracting a debt is the same as adding money.

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(All Q's of this Chapter solved)

More NCERT Questions

Try to extend this method for constructing line segments of lengths sqrt(3) and sqrt(5) using a ruler and a compass. Generalise this method to construct a line segment of any length of the form sqrt(n Consider this puzzle: What is the square root of -1? We know that 1 × 1 = 1. We also know that (-1) × (-1) = 1. There is no real number that, when multiplied by itself, results in a negative number. T The decimal expansion of p/q will be terminating precisely when the prime factors of q are only 2, only 5, or both 2 and 5. Can you explain why? [Page No. 58] Try to find the decimal expansions of 10/3 and 11/12. What do you observe about the repetition of the digits after the decimal point? [Page No. 57]