Water and wastewater · Worked step by step
What is the area of a 40 by 12 foot clarifier?
If math has never been your thing, you are in the right place. Try it on paper first, then we write it out with you, one small step at a time, and explain every step in plain words so you never lose the thread.
The problem
A rectangular clarifier floor is 40 feet long and 12 feet wide. What is the floor area?
Grab a pen and paper first
Give it a real try on paper before you watch. If you get stuck, take a hint. If you go blank, that is fine, press play and we will walk it through together.
Watch it solved, with you
Every step is written out slowly and explained in plain words, so you always know what just happened. Nobody skips ahead and leaves you behind.
Press play and I’ll write it out with you, one small step at a time.
Every step gets a plain-words explanation here, so you always know exactly what just happened and why.
The written version, step by step
- 1
Write down the two sides
length = 40 ft • width = 12 ft
- We have a rectangle, so we just need its two sides.
- Length is 40 feet, width is 12 feet.
- Both are in feet already, so nothing to convert.
- 2
Multiply length by width
area = 40 × 12 • area = 480 sq ft
- Area of a rectangle is length × width.
- 40 × 12 = 480.
- Because we multiplied feet by feet, the answer is 480 square feet.
Quick trick: 40 × 12 is 40 × 10 (=400) plus 40 × 2 (=80), which is 480. Break it up to do it in your head.
Remember this for good
The area of a rectangle is length × width. The answer is in square feet.
Picture covering the floor with 1-foot square tiles. 40 tiles along the length, 12 rows of them. 40 × 12 = 480 tiles, so 480 square feet.
Solve it fast next time
- Rectangle area = length × width. That is it.
- Area answers are always in SQUARE feet (sq ft), because you multiplied feet by feet.
- This one step is the start of most volume and loading problems, so nail it.
The answer: 480 square feet.