Question 1152848
<pre>
This is a good problem to work out mentally...

But since this is algebra.com, here is an algebraic method:
A = Alex's age

(A) + (A+5) + (A-10) = 55
3A - 5 = 55
3A = 60
A = 20   --->  A-10 = 10  (Fiona is 10)


Check:
Spelling out all the ages:
Alex is    20
Fiona is   10
Natasha is 25
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Total is   55  (ok)