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rntndnzn1 · Oct 14, 2009, 04:11 PM

Henry's bus can go just 12 miles on a gallon of gasoline. When he started his vacation, the gas tank of the bus was 5/6 full. Later when Henry had driven 336 miles, the gauge showed that the tank was still 3/5 full. If his "low on gas" light will come on when he has 1/15 of a tank remaining, how much farther can he go before seeing that light?

x/336 = (3/5 - 1/15)/(5/6 - 3/5)
x/336 = (8/15)/(7/30)
x/336 = 16/7
x = 336(16/7) = 768 miles
Is this right?

or

Is this right?
7/30 of the tank was spent going 336
miles. So the full tank should be able to provide 30/7 * 336 or 1440
miles.(It's a big tank). So 14/15 of the tank should take him 14/15 *
1440 miles = 1344 miles. Since he's already gone 336 miles, he has
1344-336 = 1008 miles to go.

Can you please tell me why which one is correct?
Thanks

Just Looking · Oct 14, 2009, 05:07 PM

Your first answer is correct. The second answer doesn't take into consideration that he started with his tank 5/6 full. It is true he can go 1440 miles on a full tank, but with 5/6 tank he can only go 5/6 X 1440 = 1200 miles. His light will come one at 1/15 of a tank, or 96 miles remaining. 1200 - 96 - 336 = 768

Unknown008 · Oct 15, 2009, 12:36 AM

Or you can do it like that:

Full tank ---> 1440 miles
8/15 of tank (remaining fraction) ----> 1440 * 8/15 = 768 miles

:)