Willie came back from Europe with 70 euros. Normally 5 euros is worth 1 dollar, but the money exchange at the airport will only give Willie 5/7ths of the official exchange rate. How many dollars does Willie get? Give the rationale and then the answer.
Let's think step by step. First first out how many euros Willie should have gotten using the official exchange rate: 70 euros / 5 euros / dollar = $14. Then multiply this quantity by 5 / 7 to find how many dollars he actually got: 14 dollars * 5 / 7 = $2 * 5 = $10.. The answer is: 10.

A sack of rice, which is 50 kilograms, costs $50. If David sells it for $1.20 per kilogram, how much will be his profit? Give the rationale and then the answer.
Let's think step by step. David's revenue for the 50 kilograms of rice is $1.20 x 50 = $60. So, his profit is $60 - $50 = $10.. The answer is: 10.

Lily has 5 lottery tickets to sell. She sells the first ticket for $1. She then sells each successive ticket for a dollar more than the previous ticket. She plans to keep a $4 profit and give the remaining money as the prize. How much money will the winner of the lottery receive? Give the rationale and then the answer.

Let's think step by step. The second ticket sold will cost $1 + $1 = $2. The third ticket sold will cost $2 + $1 = $3. The fourth ticket sold will cost $3 + $1 = $4. The fifth ticket sold will cost $4 + $1 = $5. The total money collected is $1 + $2 + $3 + $4 + $5 = $15. After taking profit, the total prize money will be $15 - $4 = $11.. The answer is: 11.