 In this video, we're going to look at how to derive equations and expressions from sentences. We can write c-5 in symbols rather than words, and the same for d times 4. But we can do much more than this. We can actually turn sentences into algebra to help us solve different problems. Like, if we have this statement, one cups cost $2.20, two cups cost $4.40, three costs $6.60, and so on. Each time, we're multiplying 220 by how many cups we want to buy. So if we wanted to buy x number of cups, we would multiply 220 by x. And in algebra, we removed the multiplication sign. So now, if we wanted 100 cups, we'd simply replace the x with 100. What if we had two sentences to write into an expression? So we're buying x adult tickets that cost 12 pounds each. So one adult cost 12, two adults cost 24, three adults cost 36. So we multiply the 12 pounds by how many adults there are. So 12x. We now need to add the children to the total cost. Can you complete the expression? 8y children. So the total cost is 12x plus 8y. A group of four adults and 10 children would cost 128 pounds. So here's one for you to do. Pause the video, give it a go. How did you get on? We can even have three or more statements involved. How could we write David's age in terms of x? David is Andrew's age x plus 8 years. What about Jane's age in terms of x? Jane is Andrew's age x doubled. So times two, which we write as 2x. Given that the total of their ages is 88, how can we use that information to find x? So we know that Andrew plus David plus Jane equals 88. And from our earlier working, replace the names with their x expressions. And we have an equation to solve. Pause the video and solve for x. Did you get x is 20? So Andrew is 20, David is 28 and Jane is 40. We just need to take these questions step by step, writing each statement into an expression. Here's one for you to try by yourself. Pause the video and give it a go. How did you get on? Can you match the phrases to the equations on expressions? Pause the video and match them up. Did you work them all out? In another video, we'll have a look at how to derive formulae such as area and volumes. If you like the video, give it a thumbs up and don't forget to subscribe. Comment below if you have any questions. Why not check out our Fuse school app as well. Until next time.