Factorise:
`xy - pq+qy-px`

Answer

To factorise the expression \( xy - pq + qy - px \), follow these steps:

### Step 1: Rearrange the terms
Rearranging the terms helps in grouping them effectively. We can write the expression as:
\[ xy - px + qy - pq \]

### Step 2: Group the terms
Now, we can group the terms into two pairs:
\[ (xy - px) + (qy - pq) \]

### Step 3: Factor out the common factors from each group
In the first group \( xy - px \), we can factor out \( x \):
\[ x(y - p) \]
In the second group \( qy - pq \), we can factor out \( q \):
\[ q(y - p) \]

### Step 4: Combine the factored groups
Now we can combine the two factored groups:
\[ x(y - p) + q(y - p) \]

### Step 5: Factor out the common binomial factor
Since \( (y - p) \) is common in both terms, we can factor it out:
\[ (y - p)(x + q) \]

### Final Answer
Thus, the factorised form of the expression \( xy - pq + qy - px \) is:
\[ (y - p)(x + q) \]

---