The number of each type Mika bought =x = 6.8 rolls; y= 2.2 rolls.
Calculation using ratio
The number of rolls of film Mika bought = 9 rolls
The number of rolls that had 36 exposures = x
The number of rolls that had 12 exposures = y
The total number of exposures = 36 + 12 = 48
To find the exposure by one roll = 48/9 = 5.3
If one roll = 5.3 exposure
x roll = 36 exposure
Make x roll the subject of formula,
x roll = 36/5.3 = 6.8 rolls
- If one roll = 5.3 exposure
y roll = 12 exposure
Make y roll the subject of formula,
y = 12/5.3 = 2.2 rolls
Therefore, the number of each type Mika bought = x = 6.8 rolls; y= 2.2 rolls.
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