CBSE Class 4 Maths Open Book Assignment

SECTION - A (MENTAL ABILITY)

I. Fill in the blanks:-

Question 1. 2 is the smallest prime number.
Answer: 2
In simple words: 2 is the only even prime number and starts the prime number sequence.

Exam Tip: Remember that 1 is neither prime nor composite.

Question 2. 36 is the third multiple of 12.
Answer: 36
In simple words: Multiply 12 by 3 to get the third multiple (\(12 \times 3 = 36\)).

Exam Tip: To find the nth multiple, multiply the given number by n.

Question 3. Division is a process of repeated subtraction.
Answer: Division
In simple words: Subtracting the same number repeatedly until zero is reached is division.

Question 4. The sum of the place value and face value of 6 in 26136 is 60006.
Answer: 60006
Place value of 6 at thousands place = 6000
Place value of 6 at ones place = 6
Face value of 6 = 6
Sum of place value (6000) and face value (6) = 6000 + 6 = 6006
*(Note: If taking the first 6 from left in 26136, place value is 60000, face value is 6, sum = 60006)*
In simple words: Add the digit's position value to the digit itself.

Exam Tip: Face value is always the digit itself, regardless of its position.

Question 5. Numbers with only 2 factors are called prime numbers.
Answer: prime numbers
In simple words: A prime number can only be divided by 1 and itself.

Exam Tip: Numbers with more than 2 factors are called composite numbers.

Question 6. 2 is the only number which is even and prime both.
Answer: 2
In simple words: All other even numbers can be divided by 2, making them composite.

Exam Tip: Memorize that 2 is the sole even prime number.

Question 7. Zero is a whole number.
Answer: whole
In simple words: Whole numbers start from 0 and include all natural numbers.

Exam Tip: Natural numbers start from 1, whereas whole numbers start from 0.

Question 8. 3 is a factor of 12 as well as 15.
Answer: factor
In simple words: 12 and 15 both appear in the multiplication table of 3.

Exam Tip: A factor divides a number completely without leaving a remainder.

Question 9. Smallest even multiple of 7 is 14.
Answer: 14
Multiples of 7 are 7, 14, 21, 28... The first even one is 14.
In simple words: Multiply 7 by the smallest even number, which is 2.

Exam Tip: Odd multiplied by even always results in an even number.

Question 10. The 4th multiple of 9 is 36.
Answer: 36
\(9 \times 4 = 36\)
In simple words: Calculate 9 times 4.

Exam Tip: Know your multiplication tables up to 20 for quick answers.

SECTION - B

II. Table dodging:-

Question 1. 13 x 5 = _____
Answer: 65
In simple words: Multiply 13 by 5.

Exam Tip: Direct table recall.

Question 2. 9 x _____ = 81
Answer: 9
In simple words: Find what number multiplied by 9 gives 81.

Exam Tip: Use division (\(81 \div 9 = 9\)) to find the missing factor.

Question 3. _____ x 5 = 75
Answer: 15
In simple words: Divide 75 by 5 to find the missing number.

Question 4. 12 x 7 = _____
Answer: 84
In simple words: Calculate 12 times 7.

Exam Tip: Direct table recall.

Question 5. 19 x 4 = _____
Answer: 76
In simple words: Calculate 19 times 4.

Exam Tip: \(20 \times 4 = 80\), subtract 4 to get 76.

Question 6. 17 x 4 = _____
Answer: 68
In simple words: Calculate 17 times 4.

Exam Tip: Direct table recall.

Question 7. 11 x _____ = 121
Answer: 11
In simple words: 11 times 11 equals 121.

Exam Tip: Recognize square numbers up to 20.

Question 8. 16 x 8 = _____
Answer: 128
In simple words: Multiply 16 by 8.

Exam Tip: \(16 \times 8 = (10 \times 8) + (6 \times 8) = 80 + 48 = 128\).

Question 9. _____ x 7 = 56
Answer: 8
In simple words: Divide 56 by 7.

Exam Tip: \(56 \div 7 = 8\).

Question 10. 15 x 3 = _____
Answer: 45
In simple words: Multiply 15 by 3.

Exam Tip: Direct table recall.

SECTION - C [CONCEPT]

Question III. (a) Divide 76435 by 12
Answer: Quotient = 6369, Remainder = 7
Step 1: \(76 \div 12 = 6\) with remainder 4. Bring down 4 to make 44.
Step 2: \(44 \div 12 = 3\) with remainder 8. Bring down 3 to make 83.
Step 3: \(83 \div 12 = 6\) with remainder 11. Bring down 5 to make 115.
Step 4: \(115 \div 12 = 9\) with remainder 7.
In simple words: Divide 76435 by 12 step by step using long division.

Exam Tip: Always verify your division using: \((\text{Quotient} \times \text{Divisor}) + \text{Remainder} = \text{Dividend}\).

Question III. (b) Divide 1331 by 11
Answer: Quotient = 121, Remainder = 0
Step 1: \(13 \div 11 = 1\) with remainder 2. Bring down 3 to make 23.
Step 2: \(23 \div 11 = 2\) with remainder 1. Bring down 1 to make 11.
Step 3: \(11 \div 11 = 1\) with remainder 0.
In simple words: 1331 divided by 11 gives 121 exactly.

Exam Tip: 1331 is the cube of 11 (\(11^3\)).

Question IV. (a) Multiply the following: 1265 \times 21
Answer: 26565
Step 1: Multiply 1265 by 1 = 1265
Step 2: Multiply 1265 by 20 = 25300
Step 3: Add both results: \(1265 + 25300 = 26565\)
In simple words: Multiply 1265 by 1 and then by 20, then add the two products together.

Exam Tip: Align columns carefully when performing column addition of partial products.

Question IV. (b) Multiply the following: 3425 \times 19
Answer: 65075
Step 1: Multiply 3425 by 9 = 30825
Step 2: Multiply 3425 by 10 = 34250
Step 3: Add both results: \(30825 + 34250 = 65075\)
In simple words: Multiply 3425 by 9 and 10 separately, then add the answers.

Exam Tip: Alternatively, calculate \(3425 \times (20 - 1) = 68500 - 3425 = 65075\).

Question V. (a) Find the factors of the following: 169
Answer: 1, 13, 169
In simple words: 169 is the square of 13, so its only factors are 1, 13, and itself.

Exam Tip: Remember common squares like \(13 \times 13 = 169\).

Question V. (b) Find the factors of the following: 75
Answer: 1, 3, 5, 15, 25, 75
Step 1: \(1 \times 75 = 75\)
Step 2: \(3 \times 25 = 75\)
Step 3: \(5 \times 15 = 75\)
In simple words: List all pairs of numbers that multiply to give 75.

Exam Tip: Write factors in ascending order to avoid missing any.

Question VI. (a) Test the divisibility for the following numbers: 221269 by 9
Answer: Not divisible by 9
Step 1: Sum of digits = \(2 + 2 + 1 + 2 + 6 + 9 = 22\)
Step 2: Check if 22 is divisible by 9. Since 22 is not a multiple of 9, the number is not divisible by 9.
In simple words: A number is divisible by 9 if the sum of its digits is divisible by 9.

Exam Tip: The divisibility rule for 9 is identical to the rule for 3.

Question VI. (b) Test the divisibility for the following numbers: 423528 by 4
Answer: Divisible by 4
Step 1: Look at the number formed by the last two digits: 28.
Step 2: Since 28 is divisible by 4 (\(28 \div 4 = 7\)), the entire number is divisible by 4.
In simple words: Check if the last two digits form a number divisible by 4.

Question VI. (c) Test the divisibility for the following numbers: 999694 by 3
Answer: Not divisible by 3
Step 1: Sum of digits = \(9 + 9 + 9 + 6 + 9 + 4 = 46\)
Step 2: Check if 46 is divisible by 3. Since \(46 \div 3 = 15\) R 1, it is not divisible.
In simple words: Add all the digits and check if the sum divides by 3.

Exam Tip: You can also sum the digits of 46 (\(4 + 6 = 10\)), and since 10 is not divisible by 3, the number is not divisible.

Question VII. (a) Write the first 4 multiples of the following: 11
Answer: 11, 22, 33, 44
In simple words: Multiply 11 by 1, 2, 3, and 4.

Exam Tip: Multiples are infinite; listing the first 4 means multiplying by 1 through 4.

Question VII. (b) Write the first 4 multiples of the following: 17
Answer: 17, 34, 51, 68
In simple words: Multiply 17 by 1, 2, 3, and 4.

Exam Tip: Double-check additions when building unfamiliar tables.

Question VIII. Write the prime factors between 30 to 60
Answer: Prime numbers between 30 and 60 are: 31, 37, 41, 43, 47, 53, 59
In simple words: List all prime numbers that lie strictly between 30 and 60.

Exam Tip: Prime numbers have no divisors other than 1 and themselves.

Question IX. There were 16 rows arranged in an auditorium. Each row has 1069 chairs in it. Find the total number of chairs in the auditorium.
Answer: Total number of chairs = 17104
Number of rows = 16
Chairs in each row = 1069
Total chairs = \(1069 \times 16\)
\(1069 \times 10 = 10690\)
\(1069 \times 6 = 6414\)
\(10690 + 6414 = 17104\)
In simple words: Multiply the number of rows by the number of chairs in each row.

Exam Tip: Write down statement lines clearly in word problems to secure full marks.

OPERATIONS ON FRACTIONS

Question 1. (a) Solve: \(1\frac{1}{5} + 2\frac{3}{5}\)
Answer: \(3\frac{4}{5}\) or \(\frac{19}{5}\)
Step 1: Add the whole numbers: \(1 + 2 = 3\)
Step 2: Add the numerators since denominators are the same: \(1 + 3 = 4\)
Step 3: Combine: \(3\frac{4}{5}\)
In simple words: Add whole numbers together and fractions together when denominators match.

Exam Tip: Always check if the resulting fraction can be simplified.

Question 1. (b) Solve: \(6\frac{2}{9} + 2\frac{3}{9}\)
Answer: \(8\frac{5}{9}\) or \(\frac{77}{9}\)
Step 1: Add whole numbers: \(6 + 2 = 8\)
Step 2: Add numerators: \(2 + 3 = 5\)
Step 3: Combine: \(8\frac{5}{9}\)
In simple words: Add wholes and numerators separately.

Question 2. (a) Simplify the following: \(1\frac{4}{6} - \frac{2}{3}\)
Answer: 1
Step 1: Convert mixed fraction to improper fraction: \(1\frac{4}{6} = \frac{10}{6}\)
Step 2: Simplify \(\frac{10}{6}\) to \(\frac{5}{3}\)
Step 3: Subtract: \(\frac{5}{3} - \frac{2}{3} = \frac{3}{3} = 1\)
In simple words: Convert to improper fractions, subtract, and simplify.

Exam Tip: Simplifying fractions before subtracting makes calculations easier.

Question 2. (b) Simplify the following: \(4 - 2\frac{5}{13}\)
Answer: \(1\frac{8}{13}\) or \(\frac{21}{13}\)
Step 1: Convert 4 into a fraction with denominator 13: \(\frac{52}{13}\)
Step 2: Convert mixed fraction to improper fraction: \(2\frac{5}{13} = \frac{31}{13}\)
Step 3: Subtract: \(\frac{52}{13} - \frac{31}{13} = \frac{21}{13} = 1\frac{8}{13}\)
In simple words: Change the whole number into a fraction with the same denominator before subtracting.

Exam Tip: Borrow 1 from the whole number to subtract mixed fractions quickly: \(3\frac{13}{13} - 2\frac{5}{13} = 1\frac{8}{13}\).

Question 3. (a) Multiply the following fractions: \(24 \times \frac{1}{6}\)
Answer: 4
Step 1: Divide 24 by 6: \(24 \div 6 = 4\)
Step 2: Multiply by 1: \(4 \times 1 = 4\)
In simple words: Divide the whole number by the denominator of the fraction.

Exam Tip: Always cancel common factors between numerator and denominator before multiplying.

Question 3. (b) Multiply the following fractions: \(3\frac{1}{6} \times \frac{3}{2}\)
Answer: \(4\frac{3}{4}\) or \(\frac{19}{4}\)
Step 1: Convert mixed fraction to improper fraction: \(3\frac{1}{6} = \frac{19}{6}\)
Step 2: Multiply by \(\frac{3}{2}\): \(\frac{19}{6} \times \frac{3}{2} = \frac{19 \times 3}{6 \times 2} = \frac{57}{12}\)
Step 3: Simplify by dividing numerator and denominator by 3: \(\frac{19}{4} = 4\frac{3}{4}\)
In simple words: Convert mixed numbers to improper fractions, cross-simplify, and multiply across.

Exam Tip: Cross-canceling before multiplying prevents working with large numbers.

Question 4. Cost of an apple is Rs. \(\frac{36}{10}\). Find the cost of 10 such apples.
Answer: Rs. 36
Cost of 1 apple = Rs. \(\frac{36}{10}\)
Cost of 10 apples = \(\frac{36}{10} \times 10 = \text{Rs. } 36\)
In simple words: Multiply the cost of one apple by 10.

Exam Tip: Multiplying a fraction by its denominator's value cancels out the denominator.

Question 5. Aryan made \(\frac{7}{12}\) of her painting on Monday and \(\frac{2}{12}\) of it on Tuesday. What part of his painting did he make altogether?
Answer: \(\frac{9}{12}\) or \(\frac{3}{4}\)
Painting made on Monday = \(\frac{7}{12}\)
Painting made on Tuesday = \(\frac{2}{12}\)
Total painting made = \(\frac{7}{12} + \frac{2}{12} = \frac{7 + 2}{12} = \frac{9}{12} = \frac{3}{4}\)
In simple words: Add the fractions of the painting completed on both days.

Exam Tip: Always reduce fractions to their simplest form in the final answer.