Calculate 15% of 60 Liters: Second Day Fuel Consumption Problem

Q: Why can't I just calculate 15% of 60 liters directly?

Because after the first day, you don't have 60 liters anymore! You only have 54 liters remaining (60 - 6 = 54). The second day's usage must be calculated from what's actually left in the tank.

Q: What if the problem asked for total fuel used over both days?

Then you would add both days together: $6 + 8.1 = 14.1$ liters total. But this specific question only asks for the second day's usage.

Q: How do I know when to use the remaining amount vs. the original amount?

Look for key phrases like 'on the second day' or 'of the remaining'. If fuel is consumed sequentially (day by day), always calculate each day's percentage from what's left after the previous day.

Q: What's the difference between this and calculating both percentages from 60?

Calculating from 60 gives: 10% of 60 = 6, and 15% of 60 = 9. But the correct way gives: 10% of 60 = 6, then 15% of 54 = 8.1. The sequential method reflects real-world fuel consumption.

Q: Can I solve this problem in a different order?

Step 1: Always calculate day 1 first (10% of 60 = 6)Step 2: Find remaining fuel (60 - 6 = 54)Step 3: Calculate day 2 from remaining (15% of 54 = 8.1)This order ensures accuracy!

Sequential Percentage Calculations with Remaining Amounts

In a car's fuel tank there are 60 liters of fuel. On the first day 10% of the fuel is used and on the second day 15% of the fuel is used.

How many liters of fuel are used on the second day?

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Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

In a car's fuel tank there are 60 liters of fuel. On the first day 10% of the fuel is used and on the second day 15% of the fuel is used.

How many liters of fuel are used on the second day?

Step-by-step solution

To solve this problem, follow these steps:

Identify original fuel quantity and calculate daily usage based on percentage.
Determine the remaining fuel after the first day's usage.
Calculate the liters used on the second day based on remaining fuel.

Let's go through the solution step-by-step:
Step 1: Calculate 10% of 60 liters (fuel used on the first day).
$\text{Fuel used on first day} = \frac{10}{100} \times 60 = 6 \text{ liters}$

Step 2: Calculate remaining fuel after the first day:
$\text{Remaining fuel} = 60 - 6 = 54 \text{ liters}$

Step 3: Calculate 15% of the remaining fuel for usage on the second day:
$\text{Fuel used on second day} = \frac{15}{100} \times 54 = 8.1 \text{ liters}$

Therefore, the amount of fuel used on the second day is 8.1 liters.

Final Answer

8.1

Key Points to Remember

Essential concepts to master this topic

Rule: Always apply the percentage to the remaining amount
Technique: Calculate step-by-step: 60 - 6 = 54, then 15% of 54
Check: Verify total usage doesn't exceed tank capacity: 6 + 8.1 = 14.1 < 60 ✓

Common Mistakes

Avoid these frequent errors

Calculating both percentages from the original 60 liters
Don't calculate 15% of 60 liters = 9 liters for the second day! This ignores that fuel was already used on day one. Always calculate the second day's percentage from the remaining fuel amount after day one.

Practice Quiz

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Calculate 15% of 100:

FAQ

Everything you need to know about this question

Why can't I just calculate 15% of 60 liters directly?

Because after the first day, you don't have 60 liters anymore! You only have 54 liters remaining (60 - 6 = 54). The second day's usage must be calculated from what's actually left in the tank.

What if the problem asked for total fuel used over both days?

Then you would add both days together: $6 + 8.1 = 14.1$ liters total. But this specific question only asks for the second day's usage.

How do I know when to use the remaining amount vs. the original amount?

Look for key phrases like 'on the second day' or 'of the remaining'. If fuel is consumed sequentially (day by day), always calculate each day's percentage from what's left after the previous day.

What's the difference between this and calculating both percentages from 60?

Calculating from 60 gives: 10% of 60 = 6, and 15% of 60 = 9. But the correct way gives: 10% of 60 = 6, then 15% of 54 = 8.1. The sequential method reflects real-world fuel consumption.

Can I solve this problem in a different order?

Step 1: Always calculate day 1 first (10% of 60 = 6)
Step 2: Find remaining fuel (60 - 6 = 54)
Step 3: Calculate day 2 from remaining (15% of 54 = 8.1)

This order ensures accuracy!

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