Answer:
In January
she used 3/5 of what she used in February.
In February she used 2/3 litres of oil.
So it is 3/5 of 2/3 to find what amount she used in January.
3/5 × 2/3 = 6/15
If we simplify 6/15 we find 2/5 as our answer.
So our answer is 2/5 litres.