You want a snack. one cookie has 130 calories. an orange has 35 calories. what is the ratio of the calories in an orange to the calories in the cookie?

We want the ratio of calories of an orange to a cookie and are told that an orange has 35 calories and a cookie has 130 so:

O:C=35:130

The greatest common factor of 35 and 130 is the product of the shared primes of the numbers prime factorization.

35=5*7 and 130=2*5*13, so the GCF is just 5, so divide each term by 5

O:C=7:26