In 21 hours, a heating plant consumes 7 liters of fuel. How much does it consume in 90 hours?
Thoughts? Step-by-step reasoning:
Let x be the consumption in 90 hours. We have: 21 / 7 = 90 / x because the heating plant always consumes fuel at the same rate. Multiplying both sides by 7x, we get 21x = 90 * 7. This can be simplified to 21x = 630. So, the consumption in 90 hours is x = 630 / 21 = 30 liters.
Thus, the answer is 30.