Question

A pair of dice numbered 1, 2, 3, 4, 5, 6 of a sixsided die and 1, 2, 3, 4 of a four-sided die is rolled and the sum is determined. Let the random variable X denote this sum. Then the number of elements in the inverse image of 7 is …

(a) 1 

(b) 2 

(c) 3 

(d) 4

Answer 1

(d) 4

Sample points to get the sum ‘7’ are (3, 4), (4, 3), (5, 2), (6, 1) 

Number of elements in inverse image of 7 = 4