Daily challenge has been designed to build healthy learning habits in kids. Math is a subject where more practice equals better knowledge retention. Science, however is more about consistent exposure to the topic in different formats of questions. The same level of consistency can be achieved with 5 engaging questions, instead of 10.
Intention of Daily Challenge for Science: mostly to help in memory and reinforcement of misconceptions and keywords. Will be repetitive to drive down keywords so there is no need for 10. 5 a day is sufficient, the key is consistent exposure.
Intention of Daily Challenge for Math: practise the skills, building the muscle to answer the questions, be familiar with the problem solving steps. Every question has different numbers, so they are learning how to apply the same skill to different scenarios, so more breadth is required. The key is practice.