Answer:
1) 30% of 60L = 18
remaining = 42 L
in 50L tank , 42/50×100 = 84%
I think there is another question you have that is like this...
If Peter used 2.8 litres of petrol daily, what percent of petrol in the 50 litre tank would be used in 10 days?
and if you do.. I got the answer to that too.
2) petrol used daily = 2.8L
10 days =2.8×10
=28L
percentage = 28/42×100
=66.6 %.
Hope it helps you.
