1 km = 1 km; 1k m = 1000m； 1 m = 10 decimeter; 1 decimeter =10cm; 1 cm =10mm.

1 m2 = 100 square decimeter; 1 square decimeter = 100 square centimeter; 1 cm2 = 100 mm2.

1 m3 = 1000 cubic decimeter; 1 cubic decimeter = 1000 cubic centimeter; 1 cubic centimeter = 1000 cubic millimeter.

1 ton = 1000 kg; 1 kg = 1 000g =1kg =2 kg.

1 hectare =10000m2; 1 mu = 666.666 square meters.

The following measures can be taken to remedy the poor mathematics in primary schools:

1, find out the problem, analyze the wrong questions, and find out the cause of the problem.

2. Use spare time to strengthen practice, make a scientific and reasonable study plan, and spend more time on math study and practice.

3. Participate in math interest classes, get in touch with more math knowledge, and expand your math vision.

4. Pay attention to mathematical thinking ability, cultivate methods such as reverse thinking and induction, and improve logical thinking and reasoning ability.

5, the habit of preview and review, review and consolidate mathematics knowledge in time, improve learning efficiency.

6, ask for help, ask teachers, parents or classmates to help review and consolidate math knowledge.

7. Change the learning method, find a method that suits you, and use charts, models and other auxiliary tools to understand and solve problems.

8. Cultivate good study habits, listen carefully in class, take notes, and review and sort out the classroom content in time.

If you want children to strengthen the foundation of primary school mathematics, you can start from the following aspects:

1, find the corresponding math tutorial class or tutorial class: taking a special math tutorial class can help you learn systematically and consolidate the basic knowledge. Cram schools usually provide targeted teaching and exercises to help you understand concepts and master skills.

2. Seek family education support: Ask your parents, relatives or family members to help you with your math. They can provide you with extra exercises, answer questions and give you guidance and encouragement in your study.

3. Use online learning resources: There are many online learning resources that can help you learn math. For example, you can find some educational websites, applications or video tutorials related to primary school mathematics. These resources usually provide interesting and interactive learning content, which can help you deepen your understanding of mathematical concepts.