इस chapter में numerical questions मुख्य रूप से
percentage, water harvesting, resource consumption,
saving और data-based applications पर आधारित हो सकते हैं।
पहले खुद solve करें, फिर solution देखें।
Percentage
Part / Whole × 100
Percentage Saving
Saving / Original × 100
Saving
Original - New
Rainwater Volume
Area × Rainfall Depth
🎯 Difficulty
20
TOTAL
4
EASY
8
HARD + VERY HARD
4
EXPERT
Numerical 1 – Percentage Use
EASY
Percentage
A village used 8000 litres of water in a day.
If 2000 litres were used for irrigation, what percentage
of the total water was used for irrigation?
Irrigation water को total water से divide करके
100 से multiply करें।
✅ Solution
Percentage = 2000/8000 × 100
Answer: 25%
Numerical 2 – Resource Saving
EASY
Conservation
A household reduced its monthly water consumption
from 20,000 litres to 15,000 litres. How much water
was saved?
Original use में से new use subtract करें।
✅ Solution
Saving = 20,000 - 15,000
Answer: 5000 litres
Numerical 3 – Percentage Saving
EASY
Water Conservation
A school reduced water use from 10,000 litres per day
to 8000 litres per day. Calculate the percentage saving.
पहले saving = 10,000 - 8,000 = 2,000.
फिर 2,000 को 10,000 से divide करें।
✅ Solution
Saving = 2000 L
Percentage saving = 2000/10000 × 100
Answer: 20%
Numerical 4 – Rainfall Conversion
EASY
Rainwater Harvesting
Rainfall of 20 mm occurs on a roof having an area of
100 m². Convert the rainfall depth into metres.
1000 mm = 1 m.
इसलिए 20 mm = 0.020 m.
✅ Solution
20 mm = 20/1000 m
Answer: 0.020 m
Numerical 5 – Rooftop Rainwater
MODERATE
Rainwater Harvesting
A roof has an area of 200 m² and receives 50 mm of rainfall.
Assuming 100% collection for this simplified calculation,
how much water falls on the roof?
50 mm = 0.05 m.
Water volume = Area × Rainfall depth.
✅ Solution
Rainfall = 50 mm = 0.05 m
Volume = 200 × 0.05
Answer: 10 m³ = 10,000 litres
Numerical 6 – Reduced Consumption
MODERATE
Resource Conservation
A family consumes 900 units of a resource annually.
After conservation measures, consumption falls to 720 units.
Find the percentage reduction.
A rooftop receives 20,000 litres of rainwater in a season.
A harvesting system collects 60% of it. How much water
is collected?
20,000 का 60% निकालना है।
✅ Solution
Collected = 0.60 × 20,000
Answer: 12,000 litres
Numerical 8 – Water Saving Per Day
MODERATE
Conservation
A conservation programme saves 250 litres of water
per day. How much water is saved in 30 days?
Daily saving × number of days.
✅ Solution
250 × 30
Answer: 7500 litres
Numerical 9 – Larger Roof
HARD
Rainwater Harvesting
A building has a roof area of 500 m². If rainfall is
80 mm and the collection efficiency is 75%, estimate
the volume of water collected.
80 mm = 0.08 m.
पहले total water volume निकालें, फिर 75% लें।
✅ Solution
Volume = 500 × 0.08 = 40 m³
Collected = 0.75 × 40
Answer: 30 m³ = 30,000 litres
Numerical 10 – Annual Saving
HARD
Resource Conservation
A school saves 120 litres of water each day after
introducing conservation measures. Estimate the annual
saving using 365 days.
Daily saving को 365 से multiply करें।
✅ Solution
120 × 365
Answer: 43,800 litres
Numerical 11 – Percentage of Annual Demand
HARD
Water Management
A community needs 500,000 litres of water annually.
Rainwater harvesting supplies 125,000 litres.
What percentage of the annual demand is met by harvesting?
Harvested water ÷ total demand × 100।
✅ Solution
125,000/500,000 × 100
Answer: 25%
Numerical 12 – Water Requirement Reduction
HARD
Conservation
A farming system reduces annual water requirement from
2 million litres to 1.5 million litres. Calculate the
amount saved and percentage reduction.
पहले 2,000,000 - 1,500,000 करें।
फिर saving ÷ original × 100।
✅ Solution
Saving = 2,000,000 - 1,500,000 = 500,000 L
Percentage = 500,000 / 2,000,000 × 100
Answer:
Saving = 500,000 L;
Reduction = 25%
Numerical 13 – Multiple Rooftops
VERY HARD
Rainwater Harvesting
Three buildings each have a roof area of 250 m².
If seasonal rainfall is 100 mm and collection efficiency
is 80%, estimate the total volume collected from all three roofs.
पहले total roof area निकालें: 250 × 3.
फिर rainfall को metres में बदलें और efficiency लगाएँ।
✅ Solution
Total area = 250 × 3 = 750 m²
100 mm = 0.10 m
Total rainfall volume = 750 × 0.10 = 75 m³
Collected = 0.80 × 75 = 60 m³
Answer: 60 m³ = 60,000 litres
Numerical 14 – Resource Efficiency
VERY HARD
Efficiency
A conservation project reduces resource use by 18%
from a starting use of 50,000 units. Find the new use.
पहले 50,000 का 18% निकालें।
फिर उसे original use से subtract करें।
✅ Solution
Saving = 0.18 × 50,000 = 9,000
New use = 50,000 - 9,000
Answer: 41,000 units
Numerical 15 – Harvesting Efficiency
VERY HARD
Rainwater Harvesting
A rooftop can theoretically collect 50,000 litres
of rainwater during a season. The actual harvesting
system collects 42,500 litres. Calculate its collection
efficiency.
Actual collection ÷ theoretical collection × 100।
✅ Solution
Efficiency = 42,500 / 50,000 × 100
Answer: 85%
Numerical 16 – Long-Term Saving
VERY HARD
Sustainable Use
A household saves 150 litres of water per day.
If the same saving continues for 4 years, estimate
the total saving using 365 days per year.
Daily × 365 × 4 करें।
✅ Solution
Annual saving = 150 × 365 = 54,750 L
Four-year saving = 54,750 × 4
Answer: 219,000 litres
Numerical 17 – Combined Conservation
EXPERT
Multiple Steps
A community uses 1,000,000 litres of water annually.
A conservation programme first reduces use by 10%.
A further project reduces the remaining use by another 15%.
Find the final annual use and total reduction.
पहले 10% reduction लगाएँ।
फिर बची हुई amount पर 15% reduction लगाएँ।
दूसरे reduction को original पर नहीं लगाना है।
✅ Step-by-Step Solution
After 10% reduction:
1,000,000 × 0.90 = 900,000 L
Second reduction:
900,000 × 0.85 = 765,000 L
Total reduction = 1,000,000 - 765,000
Answer:
Final use = 765,000 L;
Total reduction = 235,000 L
Numerical 18 – Rainwater Demand
EXPERT
Rainwater + Demand
A household requires 180,000 litres of water annually.
A rainwater harvesting system supplies 54,000 litres.
What fraction and percentage of the annual requirement
is supplied by harvested rainwater?
54,000 को 180,000 से divide करें।
फिर percentage के लिए 100 से multiply करें।
✅ Solution
Fraction = 54,000 / 180,000 = 0.3
Percentage = 0.3 × 100
Answer:
Fraction = 0.3; Percentage = 30%
Numerical 19 – Comparative Resource Use
EXPERT
Data Comparison
Town A uses 2.4 million litres of water annually
and Town B uses 1.8 million litres. By what percentage
is Town B's use lower than Town A's use?
Difference = 2.4 - 1.8 = 0.6 million.
फिर difference को Town A के use से divide करें।
✅ Solution
Difference = 2.4 - 1.8 = 0.6 million L
Percentage = 0.6/2.4 × 100
Answer: 25% lower
Numerical 20 – Final Challenge
EXPERT
Mixed Sustainable Management
A school has a roof area of 400 m². During a season,
rainfall is 150 mm and the harvesting efficiency is 80%.
The school uses 36,000 litres of water for gardening.
Calculate:
(a) harvested rainwater,
(b) percentage of gardening demand supplied by it,
and (c) remaining gardening demand.
150 mm = 0.15 m.
पहले roof पर गिरने वाला total water निकालें।
फिर 80% harvesting efficiency लगाएँ।
उसके बाद harvested water को 36,000 litres demand से compare करें।
✅ Step-by-Step Solution
(a) Total rainwater = 400 × 0.15 = 60 m³
60 m³ = 60,000 litres
Harvested = 0.80 × 60,000 = 48,000 litres
(b) Gardening demand = 36,000 litres
Percentage supplied = 48,000/36,000 × 100
= 133.33%
Since harvested water exceeds the stated gardening demand,
the full gardening demand can be met and 12,000 litres would
remain, assuming storage/use conditions allow it.
Answer:
Harvested = 48,000 L;
Demand covered = 100% of gardening need;
Surplus = 12,000 L