A farmer counts 235 caterpillars on 25 plants of a cabbage crop…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A farmer counts caterpillars on plants of a cabbage crop. The crop can bear caterpillars for each plant. If the average is higher, the farmer sprays Bacillus thuringiensis, which kills of the caterpillars that are left each day.
- What is the average number of caterpillars on a plant?
- What is the average days after the spray?
- After how many whole days is the average at or below the level that the crop can bear?
Need a reminder? The key ideaShow
Match each job to its microbe, and keep the group in mind: bacteria, fungi, a virus or cyanobacteria. An integrated pest management programme counts the pests, and acts if the average is above the level that the crop can bear. After days of spraying, a number falls to when a share of the larvae die each day.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Total: on plants. Level: . Each day are left.
Plan. Find the average, compare it with , and apply the daily factor.
Step 1. The average. . This is above , so the farmer sprays.
Step 2. After days. .
Step 3. The first day. After day the average is , which is below .
Answer: ; ; day.
Check. After days the average is , above the level, and after day it is , below it. So is the first whole day.
Watch out. Real counts vary from plant to plant. A farmer checks many plants before deciding.
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