--- title: Ages that grow together: sum and difference — a lesson of Mova's school · trees and pragmatics description: «Ages that grow together: sum and difference», a lesson of the lessons course of Mova's primary school, sentence by sentence with dependency trees and pragmatics. It begins: Each year both children get one year older, so the sum of two ages grows by 2 each year, and the difference never changes. --- [Mova](https://md.mova.elamur.ai/free/en/) · [this page in HTML](https://mova.elamur.ai/free/en/corpora/school/lessons/140-ages-sum-and-difference/) [home](https://md.mova.elamur.ai/free/en/) / [corpora](https://md.mova.elamur.ai/free/en/corpora/) / [school](https://md.mova.elamur.ai/free/en/corpora/school/) / [Lessons](https://md.mova.elamur.ai/free/en/corpora/school/lessons/) / Ages that grow together: sum and diffe… # Ages that grow together: sum and difference Lesson 140 of the lessons course of Mova's primary school: 3 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). - [0](https://md.mova.elamur.ai/free/en/corpora/school/lessons/140-ages-sum-and-difference/0/) — Each year both children get one year older, so the sum of two ages grows by 2 each year, and the difference never changes. - [1](https://md.mova.elamur.ai/free/en/corpora/school/lessons/140-ages-sum-and-difference/1/) — If two ages add up to 20 and one child is 4 years older, the younger is (20 − 4) ÷ 2 = 8. - [2](https://md.mova.elamur.ai/free/en/corpora/school/lessons/140-ages-sum-and-difference/2/) — If in 3 years the two ages will add up to 26, today they add up to 26 − 3 − 3 = 20. - ← previous: [Cuts and pieces, posts and gaps](https://md.mova.elamur.ai/free/en/corpora/school/lessons/139-cuts-and-gaps/) - next →: [Numbers to 1000: adding and taking away in stories](https://md.mova.elamur.ai/free/en/corpora/school/lessons/141-three-digit-stories/) - ↑ back to [Lessons](https://md.mova.elamur.ai/free/en/corpora/school/lessons/)