Wastewater · Worked step by step
What percent of the BOD was removed, 180 to 36?
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
Wastewater comes in with a BOD of 180 mg/L and leaves with 36 mg/L. What percent of the BOD was removed?
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The written version, step by step
- 1
Find how much was removed
removed = 180 - 36 • removed = 144 mg/L
- In at 180, out at 36.
- The difference got removed.
- 180 - 36 = 144 mg/L.
Quick trick: Removed is always in minus out.
- 2
Divide by the start, make a percent
144 ÷ 180 = 0.8 • 0.8 × 100 = 80%
- Divide removed by the starting amount: 144 ÷ 180 = 0.8.
- Times 100 to make a percent.
- So 80% of the BOD was removed.
Quick trick: 144 ÷ 180 simplifies to 4 ÷ 5, which is 0.8.
Remember this for good
Percent removed = (amount taken out divided by the amount you started with) times 100.
Removed over started, times 100. You took out 144 of the original 180, and 144 of 180 is 80 out of 100.
Solve it fast next time
- Subtract first, then divide by the starting (in) number.
- Always divide by the IN value.
- Times 100 for the percent.
The answer: 80% removed.