The average temperature on Monday, Tuesday and Wednesday was 41 °C and on Tuesday, Wednesday and Thursday it was 40 °C. If on Thursday it was exactly 39 °C, then on Monday, the temperature was

Options

A. (a) 42 °C
B. (b) 46 °C
C. (c) 23 °C
D. (d) 26 °C

Answer

To solve the problem, we will use the information given about the average temperatures over the specified days. Let's break it down step by step.

### Step 1: Define the Variables
Let:
- \( M \) = Temperature on Monday
- \( T \) = Temperature on Tuesday
- \( W \) = Temperature on Wednesday
- \( Th \) = Temperature on Thursday

### Step 2: Set Up the Equations
From the problem, we have two average temperature equations:

1. The average temperature of Monday, Tuesday, and Wednesday is 41 °C:
\[ \frac{M + T + W}{3} = 41 \]
Multiplying both sides by 3 gives:
\[ M + T + W = 123 \quad \text{(Equation 1)} \]

2. The average temperature of Tuesday, Wednesday, and Thursday is 40 °C:
\[ \frac{T + W + Th}{3} = 40 \]
Multiplying both sides by 3 gives:
\[ T + W + Th = 120 \quad \text{(Equation 2)} \]

### Step 3: Substitute the Known Value
We know from the problem that the temperature on Thursday \( Th \) is 39 °C. We can substitute this value into Equation 2:
\[ T + W + 39 = 120 \]
Subtracting 39 from both sides gives:
\[ T + W = 81 \quad \text{(Equation 3)} \]

### Step 4: Substitute Equation 3 into Equation 1
Now, we can substitute Equation 3 into Equation 1:
\[ M + (T + W) = 123 \]
Substituting \( T + W = 81 \):
\[ M + 81 = 123 \]
Subtracting 81 from both sides gives:
\[ M = 123 - 81 \]
\[ M = 42 \]

### Conclusion
The temperature on Monday was **42 °C**.

---