Question

A bottle is 80% filled with water. 36% of the water in the bottle is poured away. The volume of the water remaining in the bottle is 1.28 litres. Calculate the volume of the bottle in litres.​

Answer 1

2.5 litres

Explanation:

You want the volume of a bottle from which 36% of its contents is poured away after it was filled to 80% full, leaving 1.28 litres.

Water remaining

If 36% of the contents were poured away, then (1 -36%) = 64% of the contents remained.

If the initial contents filled the bottle to 80% full, then pouring away 36% of that contents leaves the bottle filled to ...

0.80 × 0.64 = 0.512 . . . . of its full volume

If this is 1.28 L, then the full volume is ...

0.512·V = 1.28 L

V = 1.28 L/0.512 = 2.50 L

The volume of the bottle is 2.5 litres.

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