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primary 6 | Maths
| Ratio
One Answer Below
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please help me :(
Date Posted: 4 years ago
Views: 433
When only machine A is switched on, the number of pages it printed after 20 min is not enough yet.
Machine A has to print for another 10 min.
Since 10min is half of 20 min, it means that it has to print another half of what it printed in 20 minutes, to make up for those pages machine B has not printed.
And that's equal to the amount machine B prints in 20 mins.
let what machine A prints in 20 min be 2 units.
So what it prints in 10 min
= what machine B prints in 20 min
= 2 units ÷ 2
= 1 unit
Then amount machine A prints in 30 mins = 3 x 1 unit = 3 units
So there are 3 units of pages printed in total.
Since machine B prints 1 unit in 20 min,
and there are 3 units to be printed,
3 x 20min = 60 min
Machine B will take 60 min to print all the pages alone.
Machine A has to print for another 10 min.
Since 10min is half of 20 min, it means that it has to print another half of what it printed in 20 minutes, to make up for those pages machine B has not printed.
And that's equal to the amount machine B prints in 20 mins.
let what machine A prints in 20 min be 2 units.
So what it prints in 10 min
= what machine B prints in 20 min
= 2 units ÷ 2
= 1 unit
Then amount machine A prints in 30 mins = 3 x 1 unit = 3 units
So there are 3 units of pages printed in total.
Since machine B prints 1 unit in 20 min,
and there are 3 units to be printed,
3 x 20min = 60 min
Machine B will take 60 min to print all the pages alone.
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Please understand the answer. Hope you understand that it
Date Posted:
4 years ago
Note that the pages is not actually one. It's just that A+B can print 1/20 of the pages per min, and A can print 1/30 of the pages per min.
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