Pair of Linear Equations in Two Variables — Question Ex 3.7 Q1
Back to all questionsEx 3.7 Class 10 Maths Question 1.
The age of two friends Ani and Biju differ by 3 years. Ani’s father Dharam is twice as old as Ani and Biju is twice as old as his sister Cathy. The ages of Cathy and Dharam differ by 30 years. Find the ages of Ani and Biju.
Let the ages of Ani and Biju be x years and y years respectively.
If Ani is older than Biju
x – y =3
If Biju is older than Ani
y – x = 3
-x + y =3 [Given]
Subtracting equation (i) from equation (ii), we get:
3x – 57
⇒ x = 19
Putting x = 19 in equation (i), we get
19-y = 3
⇒ y = 16
Again subtracting equation (iv) from equation (iii), we get
3x = 63
⇒ x = 21
Putting x = 21 in equation (iii) we get
21 -y= -3
⇒ y = 24
Hence, Ani’s age is either 19 years or 21 years and Biju’s age is either 16 years or 24 years.
CBSE Class 10 Pair of Linear Equations — Complete Guide
This chapter carries 5-6 marks and is crucial for the Algebra unit. Master graphical and algebraic methods for solving pairs of linear equations.
Quick Revision: Key Concepts
- Unique solution: a1/a2 ≠ b1/b2 (intersecting lines)
- Infinite solutions: a1/a2 = b1/b2 = c1/c2 (coincident lines)
- No solution: a1/a2 = b1/b2 ≠ c1/c2 (parallel lines)
- Methods: Substitution, Elimination, Cross-multiplication
- Reducible equations: Substitute u = 1/x, v = 1/y
Most Important Questions
- Determine consistency of a system of equations
- Solve using elimination or substitution method
- Word problems: age, speed, fraction, geometry type
- Equations reducible to linear form (1/x, 1/y type)
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