Hey there! This is a classic optimization problem that often trips students up because it's actually asking you to solve
two different objectives at once - and many test-takers miss this crucial detail.
Let's think about this step by step to see what's really happening here:
Step 1: Understand What We're Really OptimizingYou need to form five 2-digit numbers using each digit 0-9 exactly once, but notice the question has a double requirement:
- First: Make the sum as small as possible
- Second: Among all arrangements that achieve this minimum sum, find the largest individual number
This isn't just "find the minimum sum" - it's "find the minimum sum, THEN maximize one number within that constraint."
Step 2: Strategy for Minimum SumTo minimize the total sum, you want the smallest digits in the tens places (since tens digits contribute 10x more to the value). Ideally, you'd use digits {0,1,2,3,4} for tens places and {5,6,7,8,9} for units places.
But here's the catch - you can't have 0 as a tens digit (that would make a 1-digit number, not a 2-digit number).
So you're forced to use: {1,2,3,4,5} in tens places and {0,6,7,8,9} in units places.
Step 3: Maximize Within the ConstraintNow, to get the largest possible individual number while maintaining this minimum sum strategy:
- Largest available tens digit: 5
- Largest available units digit: 9
- Therefore, the largest possible number is 59
A complete valid arrangement would be: 10, 26, 37, 48, 59
Sum = \(10 + 26 + 37 + 48 + 59 = 180\)
Step 4: Verify This is OptimalCould we get a number in the 60s, 70s, 80s, or 90s? No - that would require putting 6, 7, 8, or 9 in a tens place, which would increase our sum beyond the minimum.
Answer: C (59)The key insight here is recognizing this as a
constrained optimization problem where you need to work within the minimum-sum constraint to find your answer.
You can check out the
complete framework and systematic approach on Neuron by e-GMAT to master constrained optimization problems and see how this pattern applies to similar questions. You can also practice with comprehensive solutions for
many other official questions here to build consistent accuracy on these multi-step optimization problems.