Answer: Fred and Phil have 720 shells altogether.
Explanation:
To solve the question, create two equations using the information supplied in the question. Solve these equations to find the number of shells that they each have then add these together. Note than 80% percent is 0.80 in decimal form.
Let Phill's number of shells be x.
Let Fred's number of shells be y.
y = 0.80x .... equation 1
x = 0.80x+80 .... equation 2
Solving equation 2:
1x-0.80x = 80
0.20x = 80
x = 80/0.20 = 400 shells
Therefore y = 0.80×400 = 320 shells.
Total = 400+320 = 720 shells.