Computer Science Chapter 4 NCERT Solutions: Introduction to Problem Solving

NCERT Solutions for Computer Science Chapter 4 Introduction To Problem Solving (2025-26): Exercise Solutions

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. Pseudocode for multiples of 5 between 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. Algorithm for collecting Rs 200 from family members in multiples of 10, 20, or 50.

Answer:

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

6. Pseudocode to print a bill including 5% GST.

Answer:

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

7. Pseudocode to compute a student's aggregate and percentage from marks.

Answer:

INPUT marks1
INPUT marks2
INPUT marks3
INPUT marks4
INPUT marks5
COMPUTE aggregate = marks1 + marks2 + marks3 + marks4 + marks5
COMPUTE percentage = (aggregate / 5)
PRINT "Aggregate:", aggregate
PRINT "Percentage:", percentage

8. Algorithm to find the greater among two user-entered numbers.

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. Algorithm: user enters a number, print GREEN/BLUE/ORANGE or message based on range.

Answer:

INPUT num
IF num >= 1 AND num <= 20 THEN
    PRINT "GREEN"
ELSE IF num >= 21 AND num <= 50 THEN
    PRINT "BLUE"
ELSE IF num >= 51 AND num <= 100 THEN
    PRINT "ORANGE"
ELSE
    PRINT "Number out of range (1-100)"

10. Algorithm to accept four numbers and find the largest and smallest.

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. Water bill calculation algorithm (tiered rates, plus meter charge).

Answer:

INPUT units
SET meter_charge = 50
IF units <= 100 THEN
    amount = units * 5
ELSE IF units <= 200 THEN
    amount = 100 * 5 + (units - 100) * 7
ELSE
    amount = 100 * 5 + 100 * 7 + (units - 200) * 10
total = amount + meter_charge
PRINT "Water bill:", total

12. What are conditionals? When are they required?

Answer: Conditionals are statements that allow a program or algorithm to make decisions based on certain conditions. They are required whenever there is a need to choose between two or more possible actions depending on whether a condition is true or false.

13. Match flowchart symbols with their functions.

14. Improve “Reach_School_Algorithm” to handle more options.

Answer: Extend the algorithm to cover multiple transport modes and traffic conditions.

Step 1: INPUT mode (Walking/Cycling/Bus/Car)
Step 2: IF mode = Walking
            PRINT "Walk via shortest route"
        ELSE IF mode = Cycling
            INPUT traffic
            IF traffic = Low THEN
                PRINT "Cycle via main road"
            ELSE
                PRINT "Cycle via side lane"
        ELSE IF mode = Bus
            INPUT time
            IF time < 8:30 THEN
                PRINT "Board regular bus"
            ELSE
                PRINT "Board express bus"
        ELSE IF mode = Car
            INPUT weather
            IF weather = Rainy THEN
                PRINT "Carry umbrella"
            PRINT "Drive safe"
Step 3: PRINT "Reached School"

15. Pseudocode for factorial of a number.

Answer:

INPUT n
SET fact = 1
SET i = 1
WHILE i <= n DO
    fact = fact * i
    i = i + 1
PRINT "Factorial is", fact

16. Flowchart for Armstrong number.

Answer: Steps for flowchart:

• Start
• Input number
• Set sum = 0, temp = number
• While temp > 0:
  • digit = temp MOD 10
  • sum = sum + digit³
  • temp = temp / 10
• If sum == number:
    Print "Armstrong number"
  Else:
    Print "Not an Armstrong number"
• End

17. Verify/correct the provided single/double/big number algorithm.

Answer: Review the provided steps to ensure correct classification. Validate for:

• If number < 10: Print "Single Digit"
• Else if number < 100: Print "Double Digit"
• Else: Print "Big Number"

18. Algorithm that accepts only positive integers up to 100. On what values will it fail?

Answer: The algorithm will fail for numbers less than 1, numbers greater than 100, and all non-integer or negative inputs (e.g., 0, -5, 101, 150, or decimal numbers).

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!