Question

While on a stakeout protecting Earth from the the universe, Agent K observed five men in black enter a coffee shop and get three doughnuts and five coffees for $3.30. Next, three aliens in disguise entered the shop and got four doughnuts and three coffees for $2.75. Finally, Agent Zed from the home office entered and got a doughnut and a cup of coffee. How much was Zed's bill? (Assume there was no tax.)

Answer 1

$ 0.8.

Explanation:

1) if to assume, 'c' - price of the coffee and 'd' - price of the doughnuts, then

2) it is possible to write the equation 1 (when five MinB enter): 3d+5c=3.3;

3) it is possible to write the equation 2 (when three aliens entered): 4d+3c=2.75;

`4) \ \left \{ {{3d+5c=3.3} \atop {4d+3c=2.75}} \right. \ = > \ \left \{ {{c=0.45} \atop {d=0.35}} \right.`

5) if c=0.45 and d=0.35, then Ag.Z. paid 0.35+0.45=$ 0.8.