SME
Grade 6 Science · Problem type
Rain collected from a roof
Use this for “How many liters of rain fall on a 10 m by 8 m roof in a 25 mm storm?”
Diagram
Rainfall: 25 mm
Water collected: 5,000 liters
This is an example. Type your own values to start a new problem.
l (m)
×
w (m)
=
A (m²)
A (m²)
×
r (mm)
=
W (liters)
Formulas
20 × 10 = 200
Roof length × roof width = roof area
200 × 25 = 5,000
Roof area × rainfall = water collected
Assumptions
•
A rain gauge measures rain as a depth in millimeters.
•
1 mm of rain on 1 square meter is exactly 1 liter of water.
•
Some water splashes or evaporates, so a barrel collects a little less.
Step-by-step
WE KNOW
Roof length: 20 m
Roof width: 10 m
Rainfall: 25 mm
FIND
roof area, water collected
Step 1 · Find roof area
20 × 10 = ?
Roof length × roof width = roof area
Length times width gives the square meters of roof.
Roof area = 200 m²
Step 2 · Find water collected
200 × 25 = ?
Roof area × rainfall = water collected
Each millimeter of rain on each square meter is 1 liter, so multiply.
Water collected = 5,000 liters
Check
Put the numbers back in. Both sides should match.
20 × 10 = 200 ✓
200 × 25 = 5,000 ✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.