HOUSEHOLD ARITHMETIC – CLASS 9 NOTES
Introduction
Household Arithmetic deals with daily life calculations such as:
Unitary method
Percentage
Electricity bill
Water bill
Telephone bill
Taxi fare
These calculations help us understand household expenses and practical mathematics.
Unitary Method
Unitary method means finding the value of one unit first and then finding the value of many units.
Example
If 12 pens cost Rs. 360
Cost of 1 pen = 360 ÷ 12 = Rs. 30
Percentage
Percentage means per hundred.
Important formulae
Percentage = (Part ÷ Whole) × 100
Increase = Add percentage
Discount = Subtract percentage
Electricity Bill Calculation
Electricity bill depends on:
Meter reading
Units consumed
Meter capacity
Tariff rate
Discount or extra charge
Units Consumed
Units consumed = Current reading − Previous reading
Meter Capacity and Minimum Charge
6–15 Ampere: Minimum charge Rs. 365 for 50 units
Electricity Tariff (Domestic)
0–50 units → Rs. 7.30 per unit
51–150 units → Rs. 8.60 per unit
151–250 units → Rs. 9.50 per unit
Above 250 units → Rs. 11.50 per unit
Discount and Fine
Paid within 7 days → 3% discount
8–22 days → No discount / no fine
23–30 days → 5% fine
31–40 days → 10% fine
41–60 days → 25% fine
Water Bill Calculation
Water bill depends on:
Pipe size
Units consumed (1 unit = 1000 litres)
Drainage charge
Payment time
For 1/2 inch pipe
Minimum consumption: 10 units
Minimum charge: Rs. 100
Extra unit charge: Rs. 32 per unit
Drainage service charge: 50%
Discount and Extra Charge
First or second month → 3% discount
Third month → No change
Fourth month → 10% fine
Fifth month → 20% fine
After fifth month → 50% fine
Telephone Bill Calculation
Local Call Tariff
First 175 calls → Rs. 200
Each additional call → Re. 1
Extra Charges
Telecommunication Service Charge (TSC) → 10%
Value Added Tax (VAT) → 13%
Taxi Fare Calculation
Day Time (6 am – 9 pm)
Minimum fare → Rs. 14
Fare per 200 meters → Rs. 7.20
Waiting charge → Rs. 7.20 per 2 minutes
Night Time (9 pm – 6 am)
Minimum fare → Rs. 21
Fare per 200 meters → Rs. 10.80
IMPORTANT SOLVED QUESTIONS (10)
Question 1
If 12 pens cost Rs. 360, find the cost of 1 pen.
Solution
Cost of 12 pens = Rs. 360
Cost of 1 pen = 360 ÷ 12 = Rs. 30
Answer: Rs. 30
Question 2
Find the total amount if 10% fine is added to Rs. 500.
Solution
Fine = 10% of 500
= (10 ÷ 100) × 500
= Rs. 50
Total amount = 500 + 50 = Rs. 550
Answer: Rs. 550
Question 3
Find the amount after 20% discount on Rs. 300.
Solution
Discount = 20% of 300
= (20 ÷ 100) × 300
= Rs. 60
Amount to pay = 300 − 60 = Rs. 240
Answer: Rs. 240
Question 4
Previous reading = 3568
Current reading = 3697
Find units consumed.
Solution
Units consumed = 3697 − 3568 = 129 units
Answer: 129 units
Question 5
If 129 units are consumed, find electricity bill (6–15A meter).
Solution
First 50 units = 50 × 7.30 = Rs. 365
Remaining units = 129 − 50 = 79
Cost of 79 units = 79 × 8.60 = Rs. 679.40
Total bill = 365 + 679.40 = Rs. 1044.40
Answer: Rs. 1044.40
Question 6
Water meter reading:
Previous = 1340, Current = 1372
Find total water bill including drainage.
Solution
Units consumed = 1372 − 1340 = 32
Minimum charge (10 units) = Rs. 100
Extra units = 22 × 32 = Rs. 704
Water bill = 100 + 704 = Rs. 804
Drainage charge = 50% of 804 = Rs. 402
Total bill = 804 + 402 = Rs. 1206
Answer: Rs. 1206
Question 7
Previous telephone reading = 2052
Current reading = 2276
Find total calls.
Solution
Total calls = 2276 − 2052 = 224
Answer: 224 calls
Question 8
Find telephone bill for 224 calls.
Solution
First 175 calls = Rs. 200
Extra calls = 224 − 175 = 49
Extra charge = 49 × 1 = Rs. 49
Call charge = 200 + 49 = Rs. 249
TSC = 10% of 249 = Rs. 24.90
VAT = 13% of (249 + 24.90) = Rs. 35.60
Total bill = Rs. 309.50
Answer: Rs. 309.50
Question 9
Taxi travels 5 km in day time with 10 minutes waiting.
Solution
Distance = 5000 m
Fare per meter = 7.20 ÷ 200
Distance fare = Rs. 180
Waiting charge = (10 ÷ 2) × 7.20 = Rs. 36
Total fare = 14 + 180 + 36 = Rs. 230
Answer: Rs. 230
Question 10
How many calls can be made with Rs. 720?
Solution
Minimum cost = Rs. 200 for 175 calls
Remaining money = 720 − 200 = Rs. 520
Extra calls = 520
Total calls = 175 + 520 = 695
Answer: 695 calls
For further practice visit this link !!
https://besidedegree.com/exam/s/academic