PSLE
Mrs Quek had a bottle of detergent. She used an equal amount of detergent each day. At the end of the eighth day, she had 480 mℓ of detergent left. At the end of the twelfth day, she had one-quarter of the bottle of detergent left. How many litres of detergent were there in the bottle at first?
Fraction of detergent used after one-quarter of the bottle was left
= 1 - ¹₄
= ³₄

³₄ of the bottle → 12 days
1 bottle → 12 ÷ ³₄ = 12 x ⁴₃ =  16 days

It takes 16 days to finish the whole bottle.

Number of days to use 480 mℓ of detergent
= 16 - 8
= 8

8 days → 480 mℓ

1 day → 480 ÷ 8 = 60 mℓ

16 days → 16 x 60 = 960 mℓ

1000 mℓ = 1 ℓ

960 mℓ = 960 ÷ 1000 = 0.96 ℓ

Volume of detergent in the bottle at first = 0.96 ℓ

Answer(s): 0.96 ℓ