PSLE
Mrs Chau had a bottle of sauce. She used an equal amount of sauce each day. At the end of the sixth day, she had 540 mℓ of sauce left. At the end of the tenth day, she had one-third of the bottle of sauce left. How many litres of sauce were there in the bottle at first?
Fraction of sauce used after one-third of the bottle was left
= 1 - ¹₃
= ²₃

²₃ of the bottle → 10 days
1 bottle → 10 ÷ ²₃ = 10 x ³₂ =  15 days

It takes 15 days to finish the whole bottle.

Number of days to use 540 mℓ of sauce
= 15 - 6
= 9

9 days → 540 mℓ

1 day → 540 ÷ 9 = 60 mℓ

15 days → 15 x 60 = 900 mℓ

1000 mℓ = 1 ℓ

900 mℓ = 900 ÷ 1000 = 0.9 ℓ

Volume of sauce in the bottle at first = 0.9 ℓ

Answer(s): 0.9 ℓ