13/20 of the group’s video games are at Jerome or Mario’s house.

Jerome has 1/4 of the group’s video games.
Mario has 2/5 of the group’s video games.

The question asks what fraction of the video games are at either of their houses. Therefore, we need to add the fractions together to find out the total fraction of the video games at both of their houses.

1/4  +  2/5
We can’t add these together because they have different denominators. We’ll need to find the least common denominator of 4 and 5 before we can add them. If you can’t think of a number that the two denominators can both multiply to get, an easy way to find the common denominator is to multiply the numbers together.

4 x 5 = 20
Therefore, our common denominator is 20. Now, we need to convert the fractions so that they can have a denominator of 20.

1/4 = ?/20
In order to find the numerator, ask yourself what we multiplied the denominator by to get the new denominator. In this case, we multiplied 4 by 5 to get 20. Therefore, we need to multiply 1 by 5 to get an equal fraction.

1 x 5 = 5
1/4 = 5/20  
Our fraction is 5/20.

2/5 = ?/20
Now, let’s do the same thing with the other fraction. In this case, we multiplied 5 by 4 to get 20, so we need to multiply 2 by 4 to get an equal fraction.

2 x 4 = 8
2/5 = 8/20
Our fraction is 8/20.

Now that the fractions both have the same denominator, we can add them together easily.

5 + 8 = 13
5/20 + 8/20 = 13/20
Add the numerators together to get the final answer.

Therefore, 13/20 of the group’s video games are either at Jerome or Mario’s house.

Hope this helps!