After an engine upgrade, a boat's still-water speed rises by 20% and its upstream speed rises by 30%. The current is 2 km/h. What was the original still-water speed?

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Accepted Answer

6 km/h. 1.2b − 2 = 1.3(b − 2) ⇒ 1.2b − 2 = 1.3b − 2.6 ⇒ 0.1b = 0.6 ⇒ b = 6 km/h. Check: upstream 4 → 5.2 km/h, a 30% rise ✓.

After an engine upgrade, a boat's still-water speed rises by 20% and its upstream speed rises by 30%. The current is 2 km/h. What was the original still-water speed?

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