Work backwards from the end using the exchange information.

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After exchange, each girl has 16 fruits and \( \frac{1}{3} \) as many apples as oranges.
• For each girl: apples : oranges = 1 : 3.
• Each girl has 4 units of fruit → 4 units = 16, 1 unit = 4.
• So each has 4 apples and 12 oranges after exchange.

Before Belle gave half her oranges to Angie:
• Belle had 12 × 2 = 24 oranges (she kept 12, gave 12 to Angie).
• Angie had 12 - 12 = 0 oranges originally.

Before Angie gave half her apples to Belle:
• Angie had 4 × 2 = 8 apples (she kept 4, gave 4 to Belle).
• Belle had 4 - 4 = 0 apples originally.

Angie bought 8 apples and Belle bought 24 oranges.
Check: Exchange → Angie: 4A+12O=16; Belle: 4A+12O=16. Ratio 4:12=1:3. ✓

Final Answer: Angie bought 8 apples, Belle bought 24 oranges.