Question

The cost of petrol rises by 2 cents per liter. Last week, a man bought 20 liters at the old price and but 10 liters and the new price. Together, all of it costs $9.20. How much is the cost of 1 liter?

Answer 1

Answer:

We suppose that a is the old price in cents

the total cost of 9.20$ equals 920 cents

so we have 20 liters bought with the old price (a) and 10 liters with the new price (a+2). This is translated into this equation where a is the old price therefore our quest to be answered

20 x a + 10 x (a+2) = 920 (cents)

20 x a + 10 x a + 20 = 920

30 x a + 20 = 920

30 x a = 920 - 20

30 x a = 900

a = 900 : 30

a = 30 (cents)

therefore the old price for 1 liter of petrol is 30 cents

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