A natural number is randomly selected from 100 to 360. Find the proba...
Total number of numbers = 360 − 100 + 1 = 261
LCM of 4,6 and 8 is equal to 24
Here, we will take 3 cases.
Case 1: Numbers divisible by 4 and 6 but not 8.
Case 2: Numbers divisible by 6 and 8 but not 4.
Case 3: Numbers divisible by 8 and 4 but not 6.
Case 1: Numbers of the form 12, (12 + 24),(12 + 2 × 24),…
From 100 to 360, the numbers are from (12 + 4 × 24) to (12 + 14 × 24) = (14 − 4 + 1) numbers = 11 numbers.
case 2:
Numbers divisible by 8 have to be divisible by 4
Hence, no number exists in this case.
case 3:
Numbers of the form 8, (8 + 24), (8 + 2 × 24),… and
16, (16 + 24), (16 + 2 × 24),…
From 100 to 360 , the numbers are from (8 + 4 × 24) to (8 + 14 × 24) and (16 + 4 × 24) to (16 + 14 × 24)
= (14 − 4 + 1) + (14 − 4 + 1) = 22
Required probability
Alternative Method:
LCM of 4,6 and 8 is equal to 24
Number of natural numbers that are divisible by 24
Number of natural numbers that are divisible by 8
= (45 − 12 − 11) = 22
Number of natural numbers that are divisible by 4
= (30 − 8 − 11) = 11
Required probability
Hence the correct option is A.