Exercise: 4-I
Mental Maths
Q1: Fill in the blanks:
i. \(\frac{7}{11}\) ____ \(\frac{5}{8}\)
Step 1: To compare, cross multiply:
\[
7 \times 8 = 56 \\
5 \times 11 = 55
\]Step 2: Since \(56 > 55\),
\[
\frac{7}{11} > \frac{5}{8}
\]Answer: \(\frac{7}{11} > \frac{5}{8}\)
ii. \(\frac{3}{7}\) ____ \(\frac{3}{5}\)
Step 1: Cross multiply:
\[
3 \times 5 = 15 \\
3 \times 7 = 21
\]Step 2: Since \(15 < 21\),
\[
\frac{3}{7} < \frac{3}{5}
\]Answer: \(\frac{3}{7} < \frac{3}{5}\)
iii. \(\frac{4}{9}\) ____ \(\frac{4}{7}\)
Step 1: Cross multiply:
\[
4 \times 7 = 28 \\
4 \times 9 = 36
\]Step 2: Since \(28 < 36\),
\[
\frac{4}{9} < \frac{4}{7}
\]Answer: \(\frac{4}{9} < \frac{4}{7}\)
iv. \(\frac{15}{4} \times\) ____ \(= \frac{3}{2}\)
Step 1: Let the blank be \(x\),
\[
\frac{15}{4} \times x = \frac{3}{2}
\]Step 2: Solve for \(x\):
\[
x = \frac{3}{2} \div \frac{15}{4} = \frac{3}{2} \times \frac{4}{15} = \frac{12}{30} = \frac{2}{5}
\]Answer: \(\frac{2}{5}\)
v. \(\frac{14}{15} \div\) ____ \(= \frac{2}{3}\)
Step 1: Let the blank be \(y\),
\[
\frac{14}{15} \div y = \frac{2}{3}
\]Step 2: Solve for \(y\):
\[
y = \frac{14}{15} \div \frac{2}{3} = \frac{14}{15} \times \frac{3}{2} = \frac{42}{30} = \frac{7}{5}
\]Answer: \(\frac{7}{5}\)
vi. Reciprocal of \(2\frac{3}{4}\) is _____
Step 1: Convert mixed fraction to improper fraction:
\[
2\frac{3}{4} = \frac{11}{4}
\]Step 2: Reciprocal is:
\[
\frac{4}{11}
\]Answer: \(\frac{4}{11}\)
Q2: Fill in the blanks:
i. \(\frac{8}{5} \div 1 =\) ______
Step 1: Dividing any number by 1 gives the number itself:
\[
\frac{8}{5} \div 1 = \frac{8}{5}
\]Answer: \(\frac{8}{5}\)
ii. \(1\frac{3}{8}\ \text{of}\ \frac{4}{5} =\) ______
Step 1: Convert mixed fraction to improper fraction:
\[
1\frac{3}{8} = \frac{11}{8}
\]Step 2: Multiply:
\[
\frac{11}{8} \times \frac{4}{5} = \frac{44}{40} = \frac{11}{10} = 1\frac{1}{10}
\]Answer: \(1\frac{1}{10}\)
iii. \(\left(\frac{5}{6}\ \text{of}\ 1\ \text{hour}\right) =\) ______ minutes
Step 1: 1 hour = 60 minutes
Step 2: Multiply:
\[
\frac{5}{6} \times 60 = 50 \text{ minutes}
\]Answer: 50 minutes
iv. \(\left(\frac{3}{8}\ \text{of}\ 1\ \text{km}\right) =\) ______ metres
Step 1: 1 km = 1000 metres
Step 2: Multiply:
\[
\frac{3}{8} \times 1000 = 375 \text{ metres}
\]Answer: 375 metres
v. \(\frac{3}{8}\ \text{of}\ ₹1 =\) ______ paise
Step 1: 1 rupee = 100 paise
Step 2: Multiply:
\[
\frac{3}{8} \times 1 = \frac{3}{8} \text{ rupees} \\
= \frac{3}{8} \times 100 = 60 \text{ paise}
\]Answer: 60 paise
Q3: Write T for true and F for false statement:
i. \(1 \div \frac{3}{2} = \frac{2}{3}\)
Step 1: Divide by a fraction = multiply by its reciprocal:
\[
1 \div \frac{3}{2} = 1 \times \frac{2}{3} = \frac{2}{3}
\]Answer: T
ii. \(1\frac{2}{3} \div \frac{3}{4} = 1\frac{1}{2}\)
Step 1: Convert mixed fraction:
\[
1\frac{2}{3} = \frac{5}{3}
\]Step 2: Divide by \(\frac{3}{4}\):
\[
\frac{5}{3} \div \frac{3}{4} = \frac{5}{3} \times \frac{4}{3} = \frac{20}{9} = 2\frac{2}{9}
\]Answer: F
iii. \(\frac{3}{5}\ \text{of}\ ₹1\ \text{kg} = 600g\)
Step 1: 1 kg = 1000 g
Step 2: Multiply:
\[
\frac{3}{5} \times 1000 = 600 \text{ g}
\]Answer: T
iv. \(\frac{3}{4} \ \text{of} \ ₹1 = 65\ \text{paise}\)
Step 1: 1 rupee = 100 paise
Step 2: Multiply:
\[
\frac{3}{4} \times 100 = 75 \text{ paise}
\]Answer: F
v. \(\frac{7}{10} \ \text{of} \ 1\ \text{hour} = 42\ \text{minutes}\)
Step 1: 1 hour = 60 minutes
Step 2: Multiply:
\[
\frac{7}{10} \times 60 = 42 \text{ minutes}
\]Answer: T
vi. \(\frac{5}{6}\ \text{and}\ \frac{5}{7}\ \text{are like fractions}\)
Step 1: Like fractions have the same denominator.
Step 2: Denominators here are 6 and 7, which are different.
Answer: F
vii. \(\frac{1}{4}\ \text{and}\ \frac{1}{5}\ \text{are unlike fractions}\)
Step 1: Unlike fractions have different denominators.
Step 2: Denominators are 4 and 5, which are different.
Answer: T