Cost price from profit or loss

Profit percent from pencil prices ●○○○○ 10 ptsThe cost price of 11 pencils is equal to the selling price of 10 pencils. Find the profit percent.
Markup rate from profit ratio ●○○○○ 10 ptsOn selling 20 units of an item, the profit is equal to the cost price of 5 units. Find the markup rate, as a percentage of the cost price.
Cost price for the first trader ●●○○○ 20 ptsA sells an item to B at a 15% profit. B sells the same item to C at a 20% profit. If C pays $1656 for it, find the price at which A bought the item.
Profit needed on remaining goods ●●○○○ 20 ptsGoods are bought for $1500. One fifth of them are sold at a loss of 15%. At what profit percentage must the rest be sold so that the overall profit is 15%?
Cost price from loss and profit ●●○○○ 20 ptsSamy sold his dining table set at a loss of 20%. If he had sold it for $800 more, he would have received a profit of 5%. Find the cost price in dollars.

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