Nanyang Pri Sch P6 CA1 2008 Math Q42

Nora bought a bottle of detergent. She used an equal amount of detergent each day. She had 2/3 of the detergent left after 5 days. She had 1.2 litres of detergent left after another 7 days. What was the volume of the detergent at first?

Solution

5 days ----- 1/3 detergent used
1 day ----- 1/3 divided by 5 = 1/15 detergent used

After another 7 days, total no. of days is 12 -----
12 days ----- 12 x (1/15) = 12/15 detergent used

Detergent left after 12 days -----
3/15 of detergent left ----- 1200 ml
1/15 detergent ----- 1200 ml divided by 3 = 400 ml
(Full amount) 15/15 ----- 15 x 400 ml = 6000 ml

Answer: 6000 ml or 6 litres were left.