Chip has a $50.00 balance on his credit card. Since he didn't pay it off, he will be charged a 20% interest fee. He puts $20.00 on his credit card the following month and doesn't make any payments to his debt. He is hit with another 20% interest fee. What's the current balance on his credit card? Give the rationale and then the answer.
Let's think step by step. He has a balance of $50.00 and is charged 20% interest so that's 50 * .20 = $10.00. He had a balance of $50.00 and now has a $10.00 interest fee making his balance 50 + 10 = $60.00. His balance is $60.00 and he puts another $20.00 on his card for a total of 60 + 20 = $80.00. He didn't make a payment that month and is hit with another 20% interest fee so that's 80 * .20 = $16.00 in interest. His new balance is 80 + 16 = $96.00.. The answer is: 96.

An author of a book got 6% of the total sales of the paper cover version of his books and 12% of the total sales of the hardcover version. If 32,000 copies of the paper cover version were sold at $0.20 each and 15,000 copies of the hardcover version were sold at $0.40 each, how much did the author earn? Give the rationale and then the answer.
Let's think step by step. The total earnings for the paper cover version were $0.20 x 32 000 = $6,400. So, the author earned $6,400 x 6 / 100 = $384 from the paper cover version. The total earnings for the hardcover version were $0.40 x 15,000 = $6,000. So, the author earned $6,000 x 12 / 100 = $720 from the hardcover version. Therefore, the author earned a total of $384 + $720 = $1104.. The answer is: 1104.

Stella and Twinkle are filling up a truck with a capacity of 6000 stone blocks at the rate of 250 blocks per hour per person. They work for four hours and are then joined by 6 other people who also work at the same rate. How many hours did filling the truck take? Give the rationale and then the answer.
Let's think step by step. Stella and Twinkle filled up the truck at the rate of 250 blocks per hour per person, a total of 2 * 250 = 500 blocks per hour for both. After working for four hours, Stella and Twinkle had filled 4 * 500 = 2000 blocks into the truck. The number of blocks they had to put into the truck for it to be full is 6000 - 2000 = 4000. When 6 more people joined Stella and Twinkle, a total of 2 + 6 = 8 people were filling the truck now. Working at the rate of 250 blocks per person, the eight people filled the truck with 250 * 8 = 2000 blocks in one hour. If there were 4000 blocks that still needed to be put into the truck, the 8 people took 4000 / 2000 = 2 hours to fill the truck with the blocks. The total time it took to fill up the tank is 4 + 2 = 6 hours.. The answer is: 6.