You have steamed 632 miles at 18.5 knots and consumed 197 tons of fuel. If you have 278 tons of usable fuel remaining, how far can you steam at 15.0 knots?
• Fuel consumption is usually based on tons of fuel per mile, not per hour • When speed changes, the distance you can travel with the same fuel depends on your fuel per mile, not directly on knots • Use the proportion: if X tons lets you go 632 miles, how many miles for 278 tons at the same consumption rate?
• First, find how many tons of fuel per mile you used on the 632-mile run • Next, assume the same consumption per mile for the remaining fuel unless told otherwise—how many miles will 278 tons give you? • Finally, check whether the change in speed from 18.5 to 15.0 knots actually affects fuel per mile in this question or is just extra information
• Be sure you divide fuel by miles, not fuel by hours, for the initial leg • Confirm that your fuel per mile number makes sense (it should be a small fraction of a ton per mile) • After finding the distance, compare with choices and ask: does any option require using the 15.0 knots value in a way that conflicts with constant fuel-per-mile consumption?
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