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primary 6 | Maths
| Fractions
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ratio of local to foreign stamps
= 5 : 4
Total = 9 units
½ of foreign stamps given to Calvin
→ 4 units x ½ = 2 units
Stamps left = 9 units - 2 units = 7 units
7 units = 252 stamps
1 unit = 252 stamps ÷ 7 = 36 stamps
So foreign stamps given to Calvin
= 2 units
= 36 stamps x 2
= 72 stamps
So ratio of local : foreign
= 3 : 1
After Thomas gave him that 72 stamps
, the ratio becomes 9 : 7
Now notice that the number of local stamps he had didn't change.
So we make the number of units the same by changing the ratio.
Ratio of local to foreign at first
= 3 : 1 = 9 : 3
We can see that the foreign stamps increased from 3 units to 7 units.
That's an increase of 4 units.
So 4 units = 72 stamps
1 unit = 72 stamps ÷ 4 = 18 stamps
Stamps Calvin had in the end
= 9 units + 7 units
= 16 units
16 x 18 stamps = 288 stamps
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