Answer: 170
==============================================
Step-by-step explanation:
A = number Ann ate
B = number Ben ate
C = number Cindy ate
Let x be some positive whole number
Since A,B,C is in the ratio 5:5:7, this means
A = 5x
B = 5x
C = 7x
Note how A:B:C = 5x:5x:7x = 5:5:7. We divide all parts by x to simplify the ratio.
-------------------
Cindy ate 30 strawberries less than Ann and Ben, so
C = A+B-30
C = 5x+5x-30
C = 10x-30
Earlier in the last section we had C = 7x, and now we found C = 10x-30
Since we're talking about the same C value, we can equate and solve
C = 7x
10x-30 = 7x ... replace C with 10x-30
10x-7x = 30
3x = 30
x = 30/3
x = 10
------------------
With this x value, we now know that...
A = 5x = 5*10 = 50
B = 5x = 5*10 = 50
C = 7x = 7*10 = 70
Cindy's count (70) is 30 less than Ann and Ben's combined count (50+50 = 100), so that helps confirm the answer.
Further confirmation comes from 50:50:70 reducing to 5:5:7 when you divide all parts by the GCF 10.
--------------------
The last step is to add the values of A, B and C.
A+B+C = 50+50+70
A+B+C = 100+70
A+B+C = 170
---------------------
Side note: since A+B+C = 5x+5x+7x = 17x, this means that the final answer is a multiple of 17.