AC Lim's answer to jayden's Primary 5 Maths Rate & Ratio Singapore question.
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Hope this helps
Date Posted:
1 year ago
We first need to decide the tank volume (for easy calculation, we choose the common multiple of 5, 6 and 3, hence 30u) as we need to know in 1 hour, how much each tap fill the tank.
As given,
Tap P fill the tank in 5 hours→ 30u
1 hour → 6u
Tap Q fill the tank in 6 hours→ 30u
1 hour → 5u
Tap R fill the tank in 3 hours→ 30u
1 hour → 10u
When all 3 tap turn on at the same time, 1 hour will fill 6u+5u +10u = 21u
To fill ½ tank = 30u÷2 = 15u=how long it takes?
21u → 1 hour
15u → 15/21 = 5/7 hour.
As given,
Tap P fill the tank in 5 hours→ 30u
1 hour → 6u
Tap Q fill the tank in 6 hours→ 30u
1 hour → 5u
Tap R fill the tank in 3 hours→ 30u
1 hour → 10u
When all 3 tap turn on at the same time, 1 hour will fill 6u+5u +10u = 21u
To fill ½ tank = 30u÷2 = 15u=how long it takes?
21u → 1 hour
15u → 15/21 = 5/7 hour.
You can check on the other tutor's answer @ Nicholas Lee.
He use tank volume as 1 unit.
So in 1 hour,
Tap P fill 1/5 tank
Tap Q fill 1/6 tank
Tap R fill 1/3 tank
When 3 tape turn on at the same time
1 hour fill 1/5+1/6+1/3 = 7/10
7/10 tank → 1 hour
1/2 tank = 1/2 ÷ 7/10 = 1/2 × 10/7 = 5/7 hour
He use tank volume as 1 unit.
So in 1 hour,
Tap P fill 1/5 tank
Tap Q fill 1/6 tank
Tap R fill 1/3 tank
When 3 tape turn on at the same time
1 hour fill 1/5+1/6+1/3 = 7/10
7/10 tank → 1 hour
1/2 tank = 1/2 ÷ 7/10 = 1/2 × 10/7 = 5/7 hour
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