Part 1:
The words Grapefruit and Watermelon have a 2:5 ratio of vowels to all the letters;
If you count, both words have 10 letters and 4 vowels so if you represent this as a ratio of vowels to total letters, it is: 4:10;
What you should know is that with ratios, you can multiply and divide each part of the ratio by a common multiplier or divisor and this will not change the ratio;
So, in the case of 4:10, we can divide both 4 and 10, by the number 2 and get the ratio 2:5;
This is the same ratio as 4:10 because we divided 4 and 10 by the same number to get it.
Part 2:
The ratio shown is of consonants to vowels;
If you count, there are a total of 17 letters, 9 are consonants and 8 are vowels, in the phrase "Eat fruit every week";
If we look at the ratio of consonants to vowels, we find it is 9:8, which matches the ratio given;
Order matters when dealing with ratios so the ratio of vowels to consonants would not be 9:8, but 8:9, which is why the given ratio has to be of consonants to vowels;
Additionally, the other two options put forth the total number of letters as one of the parts of the ratio;
There are 17 letters as I mentioned and 17 is a prime number (it cannot divide by any whole number to give another whole number) so if it was to be a part of a ratio it would have to be written as 17, which isn't the case in the ratio 9:8 as neither of these numbers are 17;
This means the two options, that say the ratio of 'all letters to ...' or '... to all letters', are definitely incorrect.