Simplify :
81 - 15.68 - 4.2

Answer

To simplify the expression \( 81 - 15.68 - 4.2 \), we can follow these steps:

### Step 1: Convert to Like Decimals
First, we need to ensure that all numbers have the same number of decimal places. The number with the most decimal places is \( 15.68 \), which has two decimal places. We can convert \( 81 \) and \( 4.2 \) to have two decimal places as well:

- \( 81 \) becomes \( 81.00 \)
- \( 4.2 \) becomes \( 4.20 \)

Now, we rewrite the expression:
\[ 81.00 - 15.68 - 4.20 \]

### Step 2: Perform the First Subtraction
Next, we will subtract \( 15.68 \) from \( 81.00 \):

\[ 81.00 - 15.68 \]

To perform this subtraction, we align the numbers:

```
81.00
- 15.68
```

Now, we subtract starting from the rightmost digit:

- In the hundredths place: \( 0 - 8 \) (we need to borrow, so it becomes \( 10 - 8 = 2 \))
- In the tenths place: \( 0 - 6 \) (after borrowing, it becomes \( 9 - 6 = 3 \))
- In the units place: \( 1 - 5 \) (we need to borrow again, so it becomes \( 11 - 5 = 6 \))
- In the tens place: \( 7 - 1 = 6 \)

So, we have:

\[ 81.00 - 15.68 = 65.32 \]

### Step 3: Perform the Second Subtraction
Now, we will subtract \( 4.20 \) from \( 65.32 \):

\[ 65.32 - 4.20 \]

Aligning the numbers again:

```
65.32
- 4.20
```

Now, we subtract:

- In the hundredths place: \( 2 - 0 = 2 \)
- In the tenths place: \( 3 - 2 = 1 \)
- In the units place: \( 5 - 4 = 1 \)
- In the tens place: \( 6 - 0 = 6 \)

So, we have:

\[ 65.32 - 4.20 = 61.12 \]

### Final Answer
The simplified result of \( 81 - 15.68 - 4.2 \) is:
\[ \boxed{61.12} \]