If ` xx ` means - , + means `-:`, - means `xx` and `-:` means + , then `15 - 2-: 900 + 90 xx 100 = ?`

Options

A. 190
B. 180
C. 90
D. -60

Explanation

To solve the expression `15 - 2 -: 900 + 90 xx 100`, we first need to interpret the operations based on the given meanings:

1. `xx` means `-`
2. `+` means `-:`
3. `-` means `xx`
4. `-:` means `+`

Now, let's rewrite the expression using these meanings:

- `15 - 2` becomes `15 xx 2` (since `-` means `xx`)
- `-:` means `+`, so `2 -: 900` becomes `2 + 900` (since `-:` means `+`)
- `+` means `-:`, so `900 + 90` becomes `900 -: 90` (since `+` means `-:`)
- `xx` means `-`, so `90 xx 100` becomes `90 - 100` (since `xx` means `-`)

Now, substituting these into the expression, we get:

`15 xx 2 + 900 -: 90 - 100`

Now, let's simplify step by step:

### Step 1: Rewrite the expression
The expression becomes:
`15 xx 2 + 900 - 90 - 100`

### Step 2: Apply the operations
Using the order of operations (BODMAS/BIDMAS), we first handle multiplication, then addition and subtraction from left to right.

1. Calculate `15 xx 2` (which is `15 * 2`):
\[ 15 * 2 = 30 \]

2. Now substitute back into the expression:
\[ 30 + 900 - 90 - 100 \]

### Step 3: Perform the addition and subtraction
1. First, add `30 + 900`:
\[ 30 + 900 = 930 \]

2. Now, subtract `90`:
\[ 930 - 90 = 840 \]

3. Finally, subtract `100`:
\[ 840 - 100 = 740 \]

### Final Result
Thus, the final answer is:
\[ \boxed{740} \]