Question 1169173
Let's break down this problem step by step.

**(a) Operating Profit/Loss During the Weekend Sale**

1.  **Calculate the Cost Price:**
    * List price: $21
    * First discount (25%): $21 * 0.25 = $5.25
    * Price after first discount: $21 - $5.25 = $15.75
    * Second discount (20%): $15.75 * 0.20 = $3.15
    * Final cost price: $15.75 - $3.15 = $12.60

2.  **Calculate the Regular Selling Price:**
    * Expenses: 20% of regular selling price
    * Profit: 17% of regular selling price
    * Total expenses + profit: 20% + 17% = 37% of regular selling price
    * Cost price represents: 100% - 37% = 63% of regular selling price
    * Regular selling price: $12.60 / 0.63 = $20

3.  **Calculate the Weekend Sale Price:**
    * Markdown: 20% of regular selling price
    * Markdown amount: $20 * 0.20 = $4
    * Weekend sale price: $20 - $4 = $16

4.  **Calculate the Operating Profit/Loss:**
    * Profit/Loss = Weekend sale price - Cost price
    * Profit/Loss = $16 - $12.60 = $3.40

    Therefore, the operating profit on the shirts sold during the weekend sale was $3.40.

**(b) Rate of Markup Realized Based on Cost**

1.  **Calculate the Markup Amount:**
    * Markup = Weekend sale price - Cost price
    * Markup = $16 - $12.60 = $3.40

2.  **Calculate the Rate of Markup Based on Cost:**
    * Rate of markup = (Markup / Cost price) * 100%
    * Rate of markup = ($3.40 / $12.60) * 100%
    * Rate of markup ≈ 26.98%

    Therefore, the rate of markup realized based on cost was approximately 26.98%.

**Final Answers:**

(a) What was the operating profit or loss on the shirts sold during the weekend sale? **$3.40 profit**

(b) What rate of markup was realized based on cost? **26.98%**