Starting with d for Dylan and b for Bailey, we see this:
d + b = 200
Then, "100 pounds more than Dylan’s weight is three times Bailey’s weight" translates to:
100 + d = 3b
Rearrange the equations to put variables in the same position:
-3b + d = -100
Flip the signs here because we want to combine by eliminating the d:
3b - d = +100 --> now add this to the other equation:
d + b = 200
------------
4b = 300, or b = 75. This implies that d = 200 - b = 125.
Answer D.Alternatively, we could of course simply solve for d in the first place, which saves a line at the end. I've chosen to eliminate d because we have the d-values scaled to the same amount, whereas we have b and 3b. We would actually lose a line here trying to scale the b-values. Remember, it's about picking your battles.
_________________
GRE / GMAT Tutor London and Online since 2005. Writer, editor, contributor for test-prep materials.
Struggling with Permutations and Combinations (Combinatorics?). I've put loads of free resources here:
https://privategmattutor.london/gmat-combinatorics-ultimate-guide-to-gmat-permutations-and-combinations/As ever, feel free to get in touch for impartial GRE / GMAT advice or to enquire about lessons at:
https://privategmattutor.london