A trader buys tea for $1200 and sells it for $1500. Per sack of tea he makes a profit of $50. How many sacks of tea did he have?

To solve this question, the user needs to know the concept of profit, which is calculated by subtracting the cost price from the selling price. The user also needs to know how to calculate the number of sacks of tea based on the given profit per sack.

Let x be the number of sacks of tea the trader had.

Total profit = selling price - cost price

$50x = $1500 - $1200

$50x = $300

x = $300/$50

x = 6

Therefore, the trader had 6 sacks of tea.

Option D is the correct answer.

Explanation for each option:

A. 4: This option is incorrect because based on the given profit per sack, the trader would have made a profit of $200 (4 x $50), which is less than the actual profit of $300.

B. 5: This option is incorrect because based on the given profit per sack, the trader would have made a profit of $250 (5 x $50), which is more than the actual profit of $300.

C. 7: This option is incorrect because based on the given profit per sack, the trader would have made a profit of $350 (7 x $50), which is more than the actual profit of $300.

The Answer is: D.