GRE Sample Test 5 Quantitative Reasoning 2

Let b = Bob’s weight and s = Sara’s weight. If Bob is currently 30 pounds heavier than Sara, then b = s + 30. If they each gain 30 pounds, then
Bob’s new weight will be b + 30 and Sara’s new weight will be s + 30. After these changes, Bob’s weight will be 25% more than Sara’s. We can translate this as: b + 30 = 1.25(s + 30). To solve for b, we should use the first equation to express s in terms of b: b = s + 30
→ b − 30 = s.
Substitute(b − 30) for s in the second equation and solve for b:
b + 30 = 1.25(b − 30 + 30)
→ b + 30 = 1.25 b
→ 30 =.25b
→ b = 120.