Reading grouped seedling lengths

The histogram shows the lengths \(l\) cm of seedlings. The five intervals are \(0\le l<5\), \(5\le l<10\), \(10\le l<15\), \(15\le l<20\) and \(20\le l<25\).

1. State the frequency for the interval from 10 cm to under 15 cm, and find the total number of seedlings.[2]
2. A seedling is ready for transplanting when its length is at least 15 cm. A gardener claims that 30% of the seedlings are ready. Use a calculation to decide whether this claim is correct.[2]
3. Explain why the histogram cannot give the exact median seedling length.[1]