To calculate the minimum marks required out of 400 to achieve above 70% in the half-yearly exams, we need to consider the weightage of each subject and the total marks allotted to that subject.

Assuming there are 5 subjects and each subject carries 80 marks, the total marks for all subjects would be 5 * 80 = 400 marks.

To achieve above 70% overall, we need to calculate the minimum marks required out of 400.

Let's break down the calculation step by step:

1. Calculate the percentage required to achieve above 70%:
- Percentage required = 70%

2. Convert the percentage to a decimal:
- Decimal form = 70/100 = 0.7

3. Calculate the total marks required out of 400:
- Total marks required = Decimal form * Total marks
- Total marks required = 0.7 * 400 = 280 marks

Hence, to achieve above 70% in the half-yearly exams, you would need a minimum of 280 marks out of 400.

Please note that this calculation assumes equal weightage for all subjects and does not take into account any additional factors such as the difficulty level of exams or individual subject requirements. It is important to focus on understanding the subject matter and performing to the best of your ability in each exam.

Summary:
- Percentage required: 70%
- Decimal form: 0.7
- Total marks required out of 400: 280 marks

280 mark is obtained