9th class pratice 1

 

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🧠 Section A: Multiple Choice Questions (1 mark each × 5 = 5 marks)

Q1. Which of the following is a valid variable name in Java?
a) 2number
b) myNumber
c) my number
d) int

Answer: b) myNumber

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Q2. Which of the following data types can store a decimal value?
a) int
b) char
c) double
d) boolean

Answer: c) double

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Q3. The Scanner class is defined in which package?
a) java.util
b) java.io
c) java.lang
d) java.text

Answer: a) java.util

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Q4. What is the result of (int) 9.7 in Java?
a) 9.0
b) 9
c) 10
d) Error

Answer: b) 9

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Q5. Which method of the Math class returns the square root of a number?
a) Math.pow()
b) Math.sqrt()
c) Math.abs()
d) Math.round()

Answer: b) Math.sqrt()

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✍️ Section B: Short Answer Questions (2 marks each × 5 = 10 marks)

Q1. Define a variable. Give one example.
Answer: A variable is a named memory location used to store a value.
Example: int age = 15;

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Q2. Differentiate between int and double data types.
Answer:

• int stores whole numbers (e.g., 5, -10).
• double stores decimal numbers (e.g., 5.5, -3.14).

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Q3. Write the steps to use the Scanner class for input.
Answer:

1. Import the class: import java.util.Scanner;
2. Create object: Scanner sc = new Scanner(System.in);
3. Take input: int num = sc.nextInt();

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Q4. What is type casting? Give an example.
Answer: Converting one data type into another.
Example:

double a = 5.7;

int b = (int)a;  // b = 5

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Q5. What will be the output of Math.max(8, 12)?
Answer: 12

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💻 Section C: Long Answer Questions (15 marks each × 4 = 60 marks)

Q1. Write a Java program to input two numbers using the Scanner class and display their sum, difference, and product.
Answer:

import java.util.*;

class Calculate {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        System.out.print("Enter first number: ");

        int a = sc.nextInt();

        System.out.print("Enter second number: ");

        int b = sc.nextInt();

        System.out.println("Sum = " + (a + b));

        System.out.println("Difference = " + (a - b));

        System.out.println("Product = " + (a * b));

    }

}

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Q2. Write a Java program to input a floating-point number and display its:
(a) Rounded value
(b) Square root
(c) Power of 3 using Math class.
Answer:

import java.util.*;

class MathExample {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        System.out.print("Enter a number: ");

        double num = sc.nextDouble();

        System.out.println("Rounded value: " + Math.round(num));

        System.out.println("Square root: " + Math.sqrt(num));

        System.out.println("Cube: " + Math.pow(num, 3));

    }

}

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Q3. Write a Java program to demonstrate type casting from double to int and int to double.
Answer:

class TypeCastingDemo {

    public static void main(String[] args) {

        double d = 9.75;

        int i = (int)d;      // Explicit casting

        int x = 10;

        double y = x;        // Implicit casting

        System.out.println("Double to int: " + i);

        System.out.println("Int to double: " + y);

    }

}

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Q4. Write a Java program to input radius and find the area and circumference of a circle using the Math class.
Answer:

import java.util.*;

class Circle {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        System.out.print("Enter radius: ");

        double r = sc.nextDouble();

        double area = Math.PI * Math.pow(r, 2);

        double circumference = 2 * Math.PI * r;

        System.out.println("Area = " + area);

        System.out.println("Circumference = " + circumference);

    }

}