We see that all three numbers are multiples of 10. So 5 and 2 are common prime factors.
Now let us find the common prime factors of 12, 21 and 27.
12=2 x 2 x 3
21=7 x 3
27=3 x 3 x 3
Thus the prime factor common to the above three numbers is 3.
So, we the following prime factors common to 120, 210 and 270
2, 3 and 5
Now let us find the rest of the common factors by multiplying the common prime factors among themselves.
2 x 3 = 6
2 x 5 = 10
3 x 5 = 15
and finally,
2 x 3 x 5 = 30.
So the factors common to 120, 210 and 270 are 2, 3, 5, 6, 10, 15, 30
There are 7 of them
The answer is
D
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