Correct Answer - Option 4 : Only D
Given:
Ratio of rainfall for 6th and 7th day = 2 ∶ 3
Average rainfall for the first five days = 0.83 cm
Average rainfall for 7 days = 0.80 cm
Formula Used:
Average = Sum of values/Number of values
Calculation:
Let the rainfall on 6th day be 2y and on 7th day be 3y
Sum of recorded rainfall for the first five days = 0.83 × 5
⇒ Sum of recorded rainfall for the first five days = 4.15
Sum of recorded rainfall for 7 days = 0.80 × 7
⇒ Sum of recorded rainfall for 7 days = 5.60
⇒ 4.15 + 2y + 3y = 5.60
⇒ 5y = 1.45
⇒ y = 0.29
Rainfall on 6th day = 2 × 0.29
⇒ 0.58 cm
Rainfall on 7th day = 3 × 0.29
⇒ 0.87 cm
⇒ n = 0.87 cm
A. n is a perfect square
0.87 is not a perfect square
⇒ A is not correct
B. n/10 is a perfect cube
0.87/10 = 0.087
⇒ B is not correct
C. n – 2 is a perfect square
0.87 – 2 = -1.13
⇒ C is not correct
D. n = 87 mm
n = 0.87 × 10 mm
⇒ 8.7 mm
⇒ D is correct
∴ Only D is correct.