Question

What's the GCF of 20 and 30

Answer 1

The preferred technique is to factor each number then multiply all common factors together to find the greatest common factor.

Explanation:

First factor 20 down to its prime factors.

2×2×5

Second factor 30 down to its prime factors

2×3×5

The common factors are 2 and 5.

The greatest common factor is 2×5=10

There are shortcuts that often work however

20 can be easily factored into 2×10 while 
30 can be easily factored into 3×10

10 can then be easily be seen as the greatest common factor.

Answer 2

10

The gcf of 20 and 30 is the largest positive integer that divides the numbers 20 and 30 without a remainder. So you can’t multiply a number higher than 10 with another number to equal 20 or to equal 30.

10*2=20
10*3=30 <- gcf

5*4=20
5*6=30 <- it can work, but it isn’t the gcf because the gcf has to be the HIGHEST number you can use to multiply with another number to equal 20 or 30

Hope this helps, love. I kinda explained it in a bad way, let me know if you need a better/simplified explanation