flasks. 24. The selling price of 15 vacuum flasks is the same as the cost of 18 vacuum (a) Let $x be the cost of a vacuum flask. Express the selling price of a vacuum flask in terms of x. (b) Using the result in (a) or otherwise, find the percentage profit in selling a vacuum flask. 25. The number of coins owned by Ann was 3 times that owned by Ben. When Ann gave 8 coins to Ben, the number of coins owned by Ann was 4 less than 2 times that owned by Ben. (a) (i) Let x be the original number of coins owned by Ben. Write an equation for x. (ii) Hence, find the final number of coins owned by Ann. (b) Find the percentage increase in the number of coins owned by Ben. 26. For the same model of smart phone, shop A sells it at a 20% profit while shop B sells it at a 25% profit. The cost $C of the smart phone is the same for both shops. (a) (i) Write down the selling price, in terms of C, in shop A. (ii) By what percentage is the selling price in shop A less than the selling price in shop B? (b) If shop A earns $200 less than shop B on selling a smart phone, find C