Final answer:
To find the rainfall in City M during May of last year, we calculate the total annual rainfall using the given average and then subtract May's contribution to find the average for the other 11 months. By setting up and solving an equation, we find that May's rainfall was 9 inches.
Step-by-step explanation:
The rainfall in City M during May of last year was three times the average monthly rainfall for the other 11 months of the year. Given that the average monthly rainfall for the entire year was 3.5 inches, we first calculate the total rainfall for the year by multiplying this average by 12 (the number of months in a year).
Total Annual Rainfall = 3.5 inches/month × 12 months = 42 inches
To find the average rainfall for the 11 months excluding May, we need to subtract May's rainfall from the total annual rainfall. Let x represent the average rainfall for the other 11 months. May's rainfall is three times x, so the equation to represent the total rainfall is:
11 × x + 3x = 42 inches
This simplifies to 14x = 42 inches, and by dividing both sides by 14, we get:
x = 3 inches
Now that we have the average for the other 11 months, we can find May's rainfall:
May's Rainfall = 3 × x = 3 × 3 inches = 9 inches
Therefore, the rainfall in City M during May was 9 inches.