---
title: "NCERT Solutions for Class 9 Maths Chapter 7 Exercise 7.4"
url: https://www.swavid.com/maths/class/9/chapter/the-mathematics-of-maybe-introduction-to-probability/ncert-solutions/exercise-7-4
dateModified: 2026-10-07T15:46:13+00:00
---

# NCERT Solutions for Class 9 Maths Chapter 7 Exercise 7.4

Chapter 7: The Mathematics of Maybe: Introduction to Probability. Every question from Exercise 7.4, with full working and the final answer.

Free PDF (20 pages): https://www.swavid.com/api/seo/pdf/ncert/maths/class-9/swavid-ncert-solutions-class-9-maths-chapter-7-the-mathematics-of-maybe-introduction-to-probability-1d9ff48bee.pdf

## Exercise Set 7.4

### Question 1

*3 marks · Short answer*

There are two fruit baskets A and B. Basket A has one apple and two oranges. Basket B has one banana and one mango. You randomly pick one fruit from each basket.
(i) Draw a tree diagram showing all possible pairs of fruits.
(ii) List the sample space.
(iii) What is the probability of picking one apple and one banana?

**Part (i)**

1. Diagram: Draw a starting point with branches to Apple, Orange (from basket A), and from each fruit, branch out to Banana and Mango (from basket B).
2. The branches represent all possible pairs of fruits chosen from the two baskets.

Answer (i): Tree diagram showing pairs from baskets A and B.

**Part (ii)**

1. List all possible pairs from the branches of the tree diagram.
2. Sample space $S = \{\text{(Apple, Banana), (Apple, Mango), (Orange, Banana), (Orange, Mango)}\}$.

Answer (ii): $S = \{\text{(Apple, Banana), (Apple, Mango), (Orange, Banana), (Orange, Mango)}\}$

**Part (iii)**

1. Identify the total number of possible outcomes, which is $4$.
2. Identify the number of favourable outcomes for picking one apple and one banana, which is $1$ (Apple, Banana).
3. Calculate the probability: $\text{P}(\text{Apple and Banana}) = \frac{1}{4} = 0.25$ or $25\%$. $\blacksquare$

Answer (iii): $\frac{1}{4}$ or $0.25$ or $25\%$

**Answer:** Tree diagram drawn, sample space listed, and probability calculated.

> Common mistake: Listing outcomes in the sample space without considering the order or missing one of the combinations.

### Question 2

*3 marks · Short answer*

Let us say that you have a box containing 3 red pens, 4 black pens and 2 green pens. You pick a pen (without looking) from the box and put it back. Then your friend does the same.
(i) What are the possible outcomes of the pen colours? Can you draw a tree diagram representing the possible outcomes?
(ii) Can you use the tree diagram to guess the probability that both you and your friend pick pens of the same colour?

**Part (i)**

1. The possible colours of the pens are Red (R), Black (BK), and Green (G).
2. Diagram: Draw a starting point with 3 main branches for R, BK, and G (your pick), and from each branch, draw 3 further branches for R, BK, and G (your friend's pick).
3. There are $3 \times 3 = 9$ possible outcomes in total.

Answer (i): Outcomes are Red, Black, Green; tree diagram with 9 branches drawn.

**Part (ii)**

1. Identify the outcomes where both pick pens of the same colour: (Red, Red), (Black, Black), and (Green, Green).
2. Count the number of favourable outcomes, which is $3$. Total possible outcomes is $9$.
3. Calculate the probability: $\text{P}(\text{same colour}) = \frac{3}{9} = \frac{1}{3} \approx 0.333$ or $33.3\%$. $\blacksquare$

Answer (ii): $\frac{1}{3}$ or $33.3\%$

**Answer:** Possible outcomes identified, tree diagram described, and probability calculated.

> Common mistake: Forgetting that pens are replaced, so the total number of options remains the same for the friend.

## Related pages

- [All Chapter 7 NCERT solutions](https://www.swavid.com/maths/class/9/chapter/the-mathematics-of-maybe-introduction-to-probability/ncert-solutions)
- [Exercise 7.1](https://www.swavid.com/maths/class/9/chapter/the-mathematics-of-maybe-introduction-to-probability/ncert-solutions/exercise-7-1)
- [Exercise 7.2](https://www.swavid.com/maths/class/9/chapter/the-mathematics-of-maybe-introduction-to-probability/ncert-solutions/exercise-7-2)
- [Exercise 7.3](https://www.swavid.com/maths/class/9/chapter/the-mathematics-of-maybe-introduction-to-probability/ncert-solutions/exercise-7-3)

Solutions written by SwaVid, a personal AI tutor for Class 6 to 10 Maths and Science. Practise this chapter free: https://www.swavid.com/start/student