The daily average rainfail on 5 days of a week is 30 mm. If the rainafail on `6^(th) and `7^(th)` day are 42 mm and 25 mm respectively. Then what is the average daily rainfail for the 7 days ?

Options

A. 31
B. 29.5
C. 33
D. 28.5

Answer

To find the average daily rainfall for 7 days, we can follow these steps:

### Step 1: Calculate the total rainfall for the first 5 days.
Given that the average rainfall for 5 days is 30 mm, we can calculate the total rainfall for these 5 days using the formula:

\[ \text{Total Rainfall for 5 days} = \text{Average Rainfall} \times \text{Number of Days} \]

\[ \text{Total Rainfall for 5 days} = 30 \, \text{mm} \times 5 = 150 \, \text{mm} \]

### Step 2: Add the rainfall for the 6th and 7th days.
The rainfall on the 6th day is 42 mm, and on the 7th day, it is 25 mm. We will add these to the total rainfall from the first 5 days:

\[ \text{Total Rainfall for 7 days} = \text{Total Rainfall for 5 days} + \text{Rainfall on 6th day} + \text{Rainfall on 7th day} \]

\[ \text{Total Rainfall for 7 days} = 150 \, \text{mm} + 42 \, \text{mm} + 25 \, \text{mm} = 217 \, \text{mm} \]

### Step 3: Calculate the average rainfall for 7 days.
Now that we have the total rainfall for 7 days, we can find the average by dividing the total rainfall by the number of days (7):

\[ \text{Average Rainfall for 7 days} = \frac{\text{Total Rainfall for 7 days}}{\text{Number of Days}} \]

\[ \text{Average Rainfall for 7 days} = \frac{217 \, \text{mm}}{7} \approx 31 \, \text{mm} \]

### Final Answer:
The average daily rainfall for the 7 days is **31 mm**.

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