Question

A girl was ask to find the L.C.M. of 3,5,12 and another number but while calculating she wrote 21 instead of 12 and yet came with correct answer. What would be the fourth number?

Answer 1

Answer:

Let the fourth number be 'a'

Suppose LCM of 3, 5, 12 and a = x

And LCM of 3, 5, 21, and a = y

Using prime factorization,

12 = 2 × 2 × 3

21 = 3 × 7

Given : x = y

So, a should contain the factors 2 × 2 ×7

Thus, a = 2 × 2 × 7 = 28

Again using prime factorization,

3 = 3

5 = 5

12 = 2 × 2 × 3

21 = 3 × 7

28 = 2 × 2 × 7

So, L. C. M. of 3, 5, 12, and 28 = 3 × 5 × 2 × 2 × 7 = 420

L. C. M. of 3, 5, 21 and  28 = 3 × 5 × 2 × 2 × 7 = 420

So, the fourth number is 28

hope this helps you...

Answer 2

Answer:

15

Step-by-step explanation:

i think it is fifteen because L.C.M of 3,5,12 = 60

and alsoL.C.M of 3,5,12,15 = 60

so.....the fourth number is 15