A gardener measures the heights of 80 seedlings in a made-up trial…

Step 1. The tallest bar. The bin 20 to 25 cm holds 28 seedlings. $\dfrac{28}{80} \times 100 = 35\%$.

Step 2. Shorter than 20 cm. The first two bins hold $6 + 14 = 20$ seedlings. $\dfrac{20}{80} \times 100 = 25\%$.

Step 3. At least 25 cm. The last two bins hold $20 + 12 = 32$ seedlings. $\dfrac{32}{80} \times 100 = 40\%$.