She will go for 7 trips if she has 15 1/2 gallons of water
<h3>Proportion and equations</h3>
From the given information, Ellen can carry
1 3/8 gallons of water each trip, this means:
In order to calculate the number of trips, it will take to make 15 1/2 gallons of water, we will have:
x = 21/2 gallons
Take the ratios of both expressions:
1/x = 11/8 * 2/21
1/x = 22/168
x = 168/22
x = 7.64 trips
Hence she will go for 7 trips if she has 15 1/2 gallons of water
Learn more on proportions here: brainly.com/question/18437927