Andros has an oil fired heating system. In 30 days period he used a full tank of oil at a constant rate per day . At a different time of the year the amount of oil andros uses per day is 1/3 of the rate used in 30 days period . How many days should a full tank of oil last at this new rate

90 days

Step-by-step explanation:

Let the rate per day for the 30 days period be x

Given that the rate drops to 1/3 of the rate used in 30 days period, it means that the new rate

= 1/3 x

If at a rate of x, the full tank runs for 30 days

at a rate of 1/3 x, the full tank would run for

= x/ (1/3 x) * 30 days

= 3 * 30 days

= 90 days

At the new rate, the full tank of oil will last for 90 days

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step-by-step explanation: