A number is mistakenly divided by 4 instead of multiplying by 4. What is the percentage change in the result due to this mistake?

In an examination, 80% of students passed in English, 70% of students passed in Hindi and 15% failed in both the subjects. What is the percentage of students who failed in only one subject?

A father said to his son, "n years back I was as old as you are now. My present age is four times your age n years back". If the sum of the present ages of the father and the son is 130 years, what is the difference of their ages?

Consider the following:

1. 1000 litres = 1 m³

2. 1 metric ton = 1000 kg

3. 1 hectare = 10,000 m²

Which of the above are correct?