1. **Problem statement:** We have two types of flour, X and Y, costing 60 and 72 per kg respectively. They are mixed to form a mixture costing 70 per kg. We need to find the ratio X:Y in the mixture. 2. **Let the quantities be:** Let the quantity of flour X be $x$ kg and flour Y be $y$ kg. 3. **Total cost equation:** The cost of the mixture per kg is given as 70, which comes from the weighted average cost: $$\frac{60x + 72y}{x + y} = 70$$ 4. **Multiply both sides by $(x + y)$:** $$60x + 72y = 70(x + y)$$ 5. **Expand the right side:** $$60x + 72y = 70x + 70y$$ 6. **Rearrange the terms to isolate x and y:** $$60x - 70x = 70y - 72y$$ $$-10x = -2y$$ 7. **Divide both sides by -2 to simplify:** $$5x = y$$ 8. **Express the ratio of X to Y:** $$\frac{x}{y} = \frac{1}{5}$$ So the ratio X:Y is 1:5. **Final answer:** The ratio of flour X to flour Y in the mixture is **1:5**.