Class 7 Maths Chapter 4 Question Answers - Expressions using Letters and Numbers

Q1: If Priya is 5 years older than Rahul, and Priya’s age is 30 years, what is Rahul’s age?

Ans: Rahul’s age = 30 – 5 = 25 years.

Q2: Simplify the expression 3x + 5x - 2x.

Ans:
Combine like terms:
= (3x + 5x - 2x) 
= (8x - 2x)
= 6x

Q3: A shop sells pencils for "c" each and erasers for "d" each. If a customer buys 4 pencils and 3 erasers, write an expression for the total cost.

Ans:
Total cost = Cost of pencils + Cost of erasers
Cost of pencils = 4 x c 
Cost of erasers =  3 x d
Total cost = 4 x c + 3 x d = 4c + 3d

Q4: If the side length of a square is "q", write the simplified algebraic expression for its perimeter.

Ans:
Perimeter = 4 x q = 4q.

Q5: If a machine takes 15 seconds to start and 5 seconds per kg to process flour, how long does it take to process 3 kg?

Ans:

Time taken by machiene= 15 + 5 × 3 
= 15 + 15 
= 30 seconds.

Q6: A rectangle has length "l" and breadth "b". Write the simplified expression for its perimeter.

Ans:
Perimeter = 2 x (l + b) 
= 2l + 2b.

Q7: Simplify Tp - p + 5q - 2q.

Ans:
Combine like terms:
(Tp - p) + (5q - 2q) 
= (Tp - p)+ 3q 

Q8: If a number machine follows the rule "3a - b", find the output when a = 5 and b = 2.

Ans: In the expression 3a - b, Put a = 5 and b = 2
Output = 3 x 5 - 2 
= 15 - 2 
= 13

Q9: A snail climbs "u" cm during the day and slips back "d" cm at night. Write an expression for its net progress after 5 days and 5 nights.

Ans:
Net progress = 5 x (u - d).

Q10: A train stops for 2 minutes at each of 3 stations. If the travel time between stations is "t" minutes, write an expression for the total journey time.

Ans:
Total time = Travel time + Stop time = 3 x t + 6 minutes.

Q11: Simplify 4(x + y) - y.

Ans:
Distribute and combine like terms:
4x + 4y - y = 4x + 3y.

Q12: If 10y - 3 and 10(y - 3) are two expressions, compare their values when y = 4.

Ans:
10y - 3 = 10 x 4 - 3 = 37.
10(y - 3) = 10 x (4 - 3) = 10.
They are not equal.

Q13: Subtract 9a - 6b + 14 from 6a + 9b - 18.

Ans:
(6a + 9b - 18) - (9a - 6b + 14) = -3a + 15b - 32.