[Question]: John buys 1.5 ounces of silver and twice as much gold. The silver costs $20 per ounce. The gold is 50 times more expensive per ounce. How much does he spend on everything?
[Answer]: He buys the silver for 1.5 * $20 = $30. He bought 1.5 * 2 = 3 ounces of gold. The gold is worth %20 * 50 = $1000 per ounce. So he buys 3 * $1000 = $3000 on gold. So he spent $30 + $3000 = $3030 on everything.
So the answer is 3030.

[Question]: In a classroom, 10 children have 7 books each. Their teacher brings another 8 books to the classroom. How many books are in the classroom altogether?
[Answer]: At first, the children have 10 * 7 = 70 books. With their teacher, they have 70 + 8 = 78 books.
So the answer is 78.

[Question]: Jack bought 3 books a month at $20 each. He sells them back at the end of the year for $500. How much money did he lose?
[Answer]:
He bought 3 * 20 = $60 of books a month. That means he bought 60 * 12 = $720 of books a year. So he lost 720 - 500 = $220.
So the answer is 220.