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2020 Math Kangaroo

Problem 25

Problem 25 · 2020 Math Kangaroo Stretch
Counting & Probability Logic & Word Problems careful-countingcasework

Ten people each order an ice cream: four vanilla, three chocolate, two lemon and one mango. As toppings they order four umbrellas, three cherries, two wafers and one chocolate gum — one topping per ice cream. Since no two of the ten ice creams may be exactly alike, which of the following combinations is possible?

Figure for Math Kangaroo 2020 Problem 25
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Answer: E — Lemon and cherry.
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Hint 1 of 2
Each flavour gets a different topping, with limited supply (4 umbrellas, 3 cherries, 2 wafers, 1 gum).
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Hint 2 of 2
A pairing is impossible if it forces two identical ice creams or runs a topping short.
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Approach: test each pairing against the flavour and topping counts
  1. Ten ice creams (4 vanilla, 3 chocolate, 2 lemon, 1 mango) each get a distinct topping (4 umbrellas, 3 cherries, 2 wafers, 1 gum), no two identical.
  2. Each option claims a specific flavour-topping pair; check it can fit a full valid assignment.
  3. Only option E (lemon with cherry) is consistent with completing the whole table.
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