NCERT Solutions For Class 11 Computer Science Chapter 4 Introduction to Problem Solving - 2025-26

Exercise

1. Write pseudocode that reads two numbers and divides one by another, displaying the quotient.

Answer:

INPUT number1
INPUT number2
COMPUTE quotient = number1 / number2
PRINT quotient

2. Coin flip cake game (see original text for full description).

Answer:

Step 1: INPUT flip1, flip2
Step 2: IF both flips are heads, THEN
    PRINT "Player 1 gets the cake"
ELSE IF both flips are tails THEN
    PRINT "Player 2 gets the cake"
ELSE
    PRINT "Cake is given to charity"

3. Write the pseudocode to print all multiples of 5 between 10 and 25 (including both 10 and 25).

Answer:

SET num = 10
WHILE num <= 25 DO
    IF num MOD 5 == 0 THEN
        PRINT num
    num = num + 1
END WHILE

4. Example of a loop executed a set number of times.

Answer: Here is a pseudocode to print "Hello" 5 times:

SET count = 1
WHILE count <= 5 DO
    PRINT "Hello"
    count = count + 1
END WHILE

5. Suppose you are collecting money for something. You need ` 200 in all. You ask your parents, uncles and aunts as well as grandparents. Different people may give either ` 10, ` 20 or even ` 50. You will collect till the total becomes 200. Write the algorithm.

Answer:

SET sum = 0
WHILE sum < 200 DO
    INPUT amount (should be 10, 20 or 50)
    sum = sum + amount
PRINT "Total collected:", sum

6. Write the pseudocode to print the bill depending upon the price and quantity of an item. Also print  Bill GST, which is the bill after adding 5% of tax in the total bill.

Answer:

INPUT amount
COMPUTE GST = amount * 0.05
COMPUTE total = amount + GST
PRINT "Bill amount with GST:", total

7. Write pseudocode that will perform the following:

1. Read the marks of three subjects: Computer

2. Science, Mathematics and Physics, out of 100

3. Calculate the aggregate marks

4. Calculate the percentage of marks

Answer:

BEGIN
    // Step a: Read marks of three subjects
    INPUT Computer_Science
    INPUT Mathematics
    INPUT Physics

    // Step b: Calculate aggregate
    Aggregate ← Computer_Science + Mathematics + Physics

    // Step c: Calculate percentage
    Percentage ← (Aggregate / 300) * 100

    // Display results
    PRINT "Aggregate Marks = ", Aggregate
    PRINT "Percentage = ", Percentage, "%"
END

8. Write an algorithm to find the greatest among two different numbers entered by the user.

Answer:

INPUT num1
INPUT num2
IF num1 > num2 THEN
    PRINT num1, "is greater"
ELSE IF num2 > num1 THEN
    PRINT num2, "is greater"
ELSE
    PRINT "Both numbers are equal"

9. Write an algorithm that performs the following:

Ask a user to enter a number. If the number is between 5 and 15, write the word GREEN. If the number is between 15 and 25, write the word BLUE. if the number is between 25 and 35, write the word ORANGE. If it is any other number, write that ALL COLOURS ARE BEAUTIFUL.

Answer:

Algorithm: Color Based on Number

Start

Input a number → num

If num >= 5 AND num < 15
→ Print "GREEN"

Else if num >= 15 AND num < 25
→ Print "BLUE"

Else if num >= 25 AND num < 35
→ Print "ORANGE"

Else
→ Print "ALL COLOURS ARE BEAUTIFUL"

End
    PRINT "Number out of range (1-100)"

10. Write an algorithm that accepts four numbers as input and find the largest and smallest of them.

Answer:

INPUT a
INPUT b
INPUT c
INPUT d
SET largest = a
IF b > largest THEN largest = b
IF c > largest THEN largest = c
IF d > largest THEN largest = d

SET smallest = a
IF b < smallest THEN smallest = b
IF c < smallest THEN smallest = c
IF d < smallest THEN smallest = d

PRINT "Largest:", largest
PRINT "Smallest:", smallest

11. Write an algorithm to display the total water bill charges of the month depending upon the number of units consumed by the customer as per the following criteria:

• for the first 100 units @ 5 per unit

• for next 150 units @ 10 per unit

• more than 250 units @ 20 per unit
  
  

Also add meter charges of 75 per month to calculate the total water bill .

Answer:

Start

Input number of units consumed → units

Initialize bill = 0

If units ≤ 100

bill = units * 5

Else if units ≤ 250

bill = (100 * 5) + (units - 100) * 10

Else (i.e., units > 250)

bill = (100 * 5) + (150 * 10) + (units - 250) * 20

Add meter charges

total_bill = bill + 75

Print total_bill

End

12. What are conditionals? When they are required in a program?

Answer: In programming, conditionals are used to apply conditions on values, inputs, or outputs. Different types of conditional statements are available to evaluate expressions. These statements usually return a result in the form of true or false, which are known as Boolean values.

13. Match flowchart symbols with their functions.

Flowchart Symbol	Functions
	Flow of Control
	Process Step
	Start/Stop of the Process
	Data
	Decision Making

Answer:

Flowchart Symbol	Functions
	Start/Stop of the Process
	Data
	Process Step
	Decision Making
	Flow of Control

14. Following is an algorithm for going to school or college. Can you suggest improvements in this to include other options?
Reach_School_Algorithm

a) Wake up

b) Get ready

c) Take lunch box

d) Take bus

e) Get off the bus

f) Reach school or college

Answer: 

Wake up early in the morning
Do light exercise or yoga
Brush teeth and wash face
Take a refreshing bath
Get dressed in school/college uniform
Eat a healthy breakfast
Pack lunch box, water bottle, and books
Revise important chapters or notes briefly
Choose transport option:
                 1. Take the school bus → get off at school stop
                 2. Or ride bicycle / walk if nearby
                 3. Or go by car/scooter with parents
Reach school/college campus
Enter classroom and get ready for studies

15. Write a pseudocode to calculate the factorial of a number (Hint: Factorial of 5, written as 5!=5 4 3 21 ×××× ) .

Answer:

BEGIN
    INPUT n
    SET fact = 1
    FOR i = 1 TO n DO
        fact = fact * i
    END FOR
    PRINT "Factorial of ", n, " = ", fact
END

16. Draw a flowchart to check whether a given number is an Armstrong number. An Armstrong number of three digits is an integer such that the sum of the cubes of its digits is equal to the number itself. For example, 371 is an Armstrong number since 3**3 +7**3 + 1**3 = 371.

Answer: 

17. Following is an algorithm to classify numbers as “Single Digit”, “Double Digit” or “Big”.

Classify_Numbers_Algo

INPUT Number

IF Number < 9

"Single Digit"

Else If Number < 99

"Double Digit"

Else

"Big"

Verify for (5, 9, 47, 99, 100 200) and correct the algorithm if required

Answer: 

Classify_Numbers_Algo

INPUT Number

IF Number <= 9

   "Single Digit"

Else If Number <= 99

   "Double Digit"

Else

   "Big"

18. For some calculations, we want an algorithm that accepts only positive integers upto 100.

Accept_1to100_Algo
INPUT Number
IF (0<= Number) AND (Number <= 100)
ACCEPT
Else
REJECT

Answer: 

(a) The algorithm fails for 0 and non-integers (like 3.5, 45.2, etc.).

(b) Improved Algorithm:

Accept_1to100_Algo
INPUT Number
IF (0<= Number) AND (Number <= 100)
ACCEPT
Else
REJECT

Mastering Problem Solving and Algorithms in Computer Science

Learning the art of problem solving and algorithm design is essential for Computer Science. This chapter guides you from identifying a problem to writing logical, step-by-step solutions perfect for exams and real-life coding tasks.

Practice using flowcharts and pseudocode for clear thinking and easy debugging. These visual and text-based tools help break down even complex questions, ensuring you are ready to tackle any kind of problem in your NCERT Solutions Computer Science exams.

Consistent revision of core concepts like input-processing-output and algorithm steps will boost your speed and accuracy. Use these smart strategies from Chapter 4 to strengthen your Computer Science fundamentals and achieve higher marks!

CBSE Class 11 Computer Science Chapter-wise NCERT Solutions

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