To add and subtract unlike fractions, find the LCM of the denominators and convert them to equivalent like fractions. You don't have to do anything to fractions to multiply them, but you may need to reduce one after multiplying. To do that, find the GCF of the numerator and the denominator and divide both of them by it. If the GCF is 1, the fraction is in its simplest form.
You have to multiply to find area you have to add to find perimiter
Knowing the LCM of the denominators will help you to find a least common denominator of unlike fractions, which will allow you to add and subtract them successfully. Knowing the GCF and LCM will not help you in multiplying them, but knowing the GCF of the numerator and denominator of a fraction will help you reduce it if necessary.
multiply first, and then add
You get the gcf and you multiply the numerator with the number you used to get to the gcf
Knowing the LCM will help when adding or subtracting unlike fractions. By finding the LCM of the denominators, (called the lowest common denominator) you can convert unlike to like fractions and proceed with the adding or subtracting. Knowing the GCF helps reduce a fraction. By finding the GCF of the numerator and the denominator and dividing both of them by it, you can reduce a fraction to its lowest terms (simplest form). If the GCF is 1, the fraction is in its simplest form. You can successfully multiply fractions without knowing the GCF or LCM.
GCF is a single number. You can't add a GCF.
When adding and subtracting unlike fractions, it is necessary to find a least common denominator. It's the same process as finding an LCM. You can simplify a fraction by finding the GCF of the numerator and denominator and dividing them both by it.
You multiply them.
You multiply (or divide), not add.
you can multiply 281 and 3 you can add 840 and 3
you are suppose to MULTIPLY on area.
Both. Add the hours and then multiply by the money
You add for perimeter...