LCD/LCM story: (LCD is not a computer monitor here) ;-)
"Least common denominator of 2 or more whole numbers (integers) is the smallest positive whole number that is a multiple of those numbers."
Here's one application of LCD/LCM. When you're adding or subtracting fractions you must make your denominators the same.
2
+
1
=
2×2
+
1×3
=
4
+
3
=
4 + 3
=
7
3
2
3×2
2×3
6
6
6
6
=> that's when you do go for LCD/LCM, and in this case your LCD = 6
GCF/GCD story:
"Greatest common factor of 2 or more non-zero whole numbers (integers), is the biggest positive number that divides those numbers without a remainder."
And when you're trying to put something in front of parentheses, say:
6a + 3b = 3×(2a + b)
=> that's when you do go for GCF (Greatest Common Factor), and in this case your GCF = 3