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primary 6 | Maths
| Ratio
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Please help!!i try this so many times ,but i can't solve it ! Please help me !!
Let the number of 50-dollar notes be 1 unit. Then the number of 20-dollar notes is 6 units and the number of 50-dollar notes is 3 units.
Total value of 50-dollar notes
= 50-dollar x 1 unit
= 50 dollar-units
Total value of 20-dollar notes
= 20-dollar x 6 units
= 120 dollar-units
Total value of 10-dollar notes
= 10-dollar x 3 units
= 30 dollar-units
Total value of all the notes
= 50 + 120 + 30
= 200 dollar-units
This corresponds to a total of $1600.
200 dollar-units = $1600
1 dollar-unit = $1600/200 = $8
50 dollar-units = $8 x 50 = $400
120 dollar-units = $8 x 120 = $960
30 dollar-units = $8 x 30 = $240
Number of 50-dollar notes
= 400/50
= 8
Number of 20-dollar notes
= 960/20
= 48
Number of 10-dollar notes
= 240/10
= 24
*******************************
Now, she sold 1/3 of the 10-dollar notes and some 20-dollar notes. No 50-dollar notes have been sold away. The 50-dollar notes make up 2/13 of the total number of notes at the end.
Since she sold 1/3 of the 10-dollar notes, she must have sold 1/3 x 24 = 8 pieces of 10-dollar notes.
There are 8 pieces of 50-dollar notes and this makes up 2/13 of the total number of notes at the end.
2 units = 8 pieces
1 unit = 8/2 = 4 pieces
13 units = 4 x 13 = 52 pieces
11 units = 4 x 11 = 44 pieces
So there are a total of 44 pieces of 10-dollar and 20-dollar notes at the end.
Compare this with the 48 + 24 = 72 pieces of 10-dollar and 20-dollar notes at the start.
This shows that a total of 72 - 44 = 28 pieces of 10-dollar and 20-dollar notes have been sold.
But earlier we found that 8 pieces of 10-dollar notes have been sold.
Number of 20-dollar notes sold
= 28 - 8
= 20
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