NCERTCh 4Free

Chapter 4

🎓 Class 8📖 Mathematics📖 5 notes🧠 15 Q&A⏱️ ~8 min

Chapter 4Study Notes

NCERT-aligned · 5 notes · 3 shown free

Looking for Information

Explanation

Looking for Information

This section introduces the fundamental concept of gathering and interpreting information, which is essential in mathematics and everyday life. It emphasizes that information can be numerical, textual, or graphical and that understanding how to look for and analyze information is crucial for solving problems effectively. The chapter begins by highlighting the importance of data collection and the various sources from which information can be obtained, such as surveys, experiments, observations, and secondary data from books or the internet. It explains that before solving any mathematical problem, one must carefully read and comprehend the problem statement to identify the relevant information. The section also discusses the role of organizing information systematically to make it easier to analyze. It introduces the idea that data can be represented in different forms like tables, charts, or graphs to facilitate understanding and comparison. The section sets the stage for learning how to interpret data and use it to find solutions, stressing that looking for information is the first step in problem-solving and decision-making processes.

  • Information can be numerical, textual, or graphical.
  • Sources of information include surveys, experiments, observations, and secondary data.
  • Understanding the problem statement is essential to identify relevant information.
  • Organizing data systematically helps in better analysis.
  • Data representation through tables and graphs aids comprehension.
  • Looking for information is the first step in problem-solving.
  • 📌 Information: Data or facts collected for reference or analysis.
  • 📌 Data: Raw facts or figures collected from observations or measurements.
  • 📌 Survey: A method of collecting data by asking questions to a group of people.

Organising Data

Explanation

Organising Data

This section focuses on the methods of organizing collected data so that it becomes meaningful and easier to analyze. It explains that raw data, when arranged systematically, can reveal patterns and relationships that are not obvious otherwise. The section introduces the concept of a data table as a primary tool for organizing information. It details how to classify data into categories or classes and record the frequency of each category. The importance of clear labeling of rows and columns in tables is emphasized to avoid confusion. The section also discusses the difference between qualitative data (non-numerical, such as colors or names) and quantitative data (numerical, such as heights or ages), and how each type can be organized. It explains that organizing data is essential before representing it graphically or performing any calculations. The section also introduces the concept of tally marks as a simple method to count frequencies during data collection. By the end of the section, students understand how to convert raw data into a structured format that can be easily interpreted and used for further analysis.

  • Organizing data helps reveal patterns and relationships.
  • Data tables are used to arrange information systematically.
  • Classification involves grouping data into categories or classes.
  • Frequency is the count of data items in each category.
  • Qualitative data is non-numerical; quantitative data is numerical.
  • Tally marks are a simple way to record frequencies.
  • 📌 Classification: Grouping data into categories based on shared characteristics.
  • 📌 Frequency: The number of times a particular data value occurs.
  • 📌 Tally marks: A counting method using vertical lines grouped in fives.

Representing Data

Explanation

Representing Data

This section explains how to represent organized data visually to make it easier to understand and interpret. It introduces different graphical methods such as bar graphs, pictographs, and pie charts. The section explains that graphical representatio

Practice QuestionsChapter 4

Includes NCERT exercise questions with answers

Q1.1. A survey was made to find the type of music that a certain group of young people liked in a city. Adjoining pie chart shows the findings of this survey. From this pie chart answer the following: (i) If 20 people liked classical music, how many young people were surveyed? (ii) Which type of music is liked by the maximum number of people? (iii) If a cassette company were to make 1000 CD's, how many of each type would they make?

Answer:

Solution: Let the total number of young people surveyed be N. (i) From the pie chart, classical music sector corresponds to 90°. Since total angle in pie chart = 360°, the fraction of people liking classical music = 90/360 = 1/4. Given number of people liking classical music = 20. So, (1/4) * N = 20 => N = 20 * 4 = 80. Therefore, total number of young people surveyed = 80. (ii) From the pie chart, the sector with the largest angle corresponds to pop music (120°). Hence, pop music is liked by the maximum number of people. (iii) Total CDs to be made = 1000. Number of CDs for each type = (central angle / 360) * 1000. - Classical (90°): (90/360)*1000 = 250 CDs - Pop (120°): (120/360)*1000 = 333 CDs - Rock (60°): (60/360)*1000 = 167 CDs - Jazz (30°): (30/360)*1000 = 83 CDs - Folk (60°): (60/360)*1000 = 167 CDs (If fractions arise, round appropriately.)

Explanation:

The pie chart represents the distribution of music preferences in terms of central angles. Using the proportion of the central angle to the full circle (360°), we calculate the fraction of people liking each music type. Multiplying this fraction by the total number of people gives the count for each category. For part (i), we use the given number of people liking classical music to find the total surveyed. For part (iii), the same fraction is applied to the total CDs to be produced.

MediumNCERT
Q2.2. A group of 360 people were asked to vote for their favourite season from the three seasons rainy, winter and summer. (i) Which season got the most votes? (ii) Find the central angle of each sector. (iii) Draw a pie chart to show this information.

Answer:

Solution: Given total people = 360 Votes: - Summer = 90 - Rainy = 120 - Winter = 150 (i) Season with most votes = Winter (150 votes). (ii) Central angle for each sector = (Number of votes / Total votes) * 360° - Summer: (90/360)*360 = 90° - Rainy: (120/360)*360 = 120° - Winter: (150/360)*360 = 150° (iii) To draw the pie chart: - Draw a circle. - Use a protractor to measure and draw sectors of 90°, 120°, and 150° corresponding to Summer, Rainy, and Winter respectively. - Label each sector accordingly.

Explanation:

The central angle of each sector in a pie chart is proportional to the fraction of the total votes that season received. By multiplying the fraction by 360°, we get the angle for each sector. The season with the highest votes has the largest central angle.

MediumNCERT
Q3.3. Draw a pie chart showing the following information. The table shows the colours preferred by a group of people. Colours: Blue - 18, Green - 9, Red - 6, Yellow - 3, Total - 36

Answer:

Solution: Total number of people = 36 Calculate central angle for each colour: - Blue: (18/36)*360 = 180° - Green: (9/36)*360 = 90° - Red: (6/36)*360 = 60° - Yellow: (3/36)*360 = 30° To draw the pie chart: - Draw a circle. - Use a protractor to mark sectors of 180°, 90°, 60°, and 30° for Blue, Green, Red, and Yellow respectively. - Label each sector with the colour name and number of people.

Explanation:

The central angle for each sector is proportional to the number of people preferring that colour. Multiplying the fraction by 360° gives the angle for each sector. Drawing the sectors with these angles gives the pie chart.

EasyNCERT
Q4.4. The adjoining pie chart gives the marks scored in an examination by a student in Hindi, English, Mathematics, Social Science and Science. If the total marks obtained by the students were 540, answer the following questions. (i) In which subject did the student score 105 marks? (Hint: for 540 marks, the central angle = 360°. So, for 105 marks, what is the central angle?) (ii) How many more marks were obtained by the student in Mathematics than in Hindi? (iii) Examine whether the sum of the marks obtained in Social Science and Mathematics is more than that in Science and Hindi. (Hint: Just study the central angles).

Answer:

Solution: Total marks = 540 Central angle for total marks = 360° (i) Central angle corresponding to 105 marks = (105/540)*360 = 70° From the pie chart, the sector with 70° corresponds to English. Therefore, the student scored 105 marks in English. (ii) Marks in Mathematics correspond to 120°. Marks in Hindi correspond to 90°. Marks in Mathematics = (120/360)*540 = 180 Marks in Hindi = (90/360)*540 = 135 Difference = 180 - 135 = 45 marks (iii) Marks in Social Science = 90° => (90/360)*540 = 135 Marks in Mathematics = 180 (from above) Sum = 135 + 180 = 315 Marks in Science = 60° => (60/360)*540 = 90 Marks in Hindi = 135 (from above) Sum = 90 + 135 = 225 Since 315 > 225, the sum of marks in Social Science and Mathematics is more than that in Science and Hindi.

Explanation:

The central angle in the pie chart is proportional to the marks obtained in each subject. Using the ratio of marks to total marks multiplied by 360°, we find the central angle or marks for each subject. Comparing these helps answer the questions.

MediumNCERT
Q5.5. The number of students in a hostel, speaking different languages is given below. Display the data in a pie chart. Language: Hindi - 40, English - 12, Marathi - 9, Tamil - 7, Bengali - 4, Total - 72

Answer:

Solution: Total students = 72 Calculate central angle for each language: - Hindi: (40/72)*360 = 200° - English: (12/72)*360 = 60° - Marathi: (9/72)*360 = 45° - Tamil: (7/72)*360 = 35° - Bengali: (4/72)*360 = 20° To draw the pie chart: - Draw a circle. - Use a protractor to mark sectors of 200°, 60°, 45°, 35°, and 20° for Hindi, English, Marathi, Tamil, and Bengali respectively. - Label each sector with the language and number of students.

Explanation:

The central angle for each sector is proportional to the number of students speaking that language. Multiplying the fraction by 360° gives the angle for each sector. Drawing the sectors with these angles gives the pie chart.

MediumNCERT
Q6.TRY THESE 1. If you try to start a scooter, what are the possible outcomes?

Answer:

Possible outcomes when you try to start a scooter are: - The scooter starts. - The scooter does not start.

Explanation:

The experiment of trying to start a scooter has two possible outcomes: success (starts) or failure (does not start).

EasyNCERT
Q7.2. When a die is thrown, what are the six possible outcomes?

Answer:

The six possible outcomes when a die is thrown are: 1, 2, 3, 4, 5, and 6.

Explanation:

A die has six faces numbered from 1 to 6, so these are the possible outcomes of a throw.

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Q8.3. When you spin the wheel shown, what are the possible outcomes? (Fig 4.6) List them. (Outcome here means the sector at which the pointer stops).

Answer:

Possible outcomes are the sectors where the pointer can stop. From Fig 4.6, the sectors are numbered 1, 2, 3, 4, 5, and 6. Hence, the possible outcomes are: 1, 2, 3, 4, 5, 6.

Explanation:

Each sector on the wheel represents a possible outcome when the wheel is spun. The pointer can stop at any one of these sectors.

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