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Given a list of conversion items between symbols, write an algorithm to return the conversion ratio for each pair of symbols.

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Calculate Conversion Ratios. Given a list of conversion pairs between different units of measurement, write an algorithm that returns the conversion ratio from one unit to another, either directly or through a series of conversions. If no conversion is possible, the algorithm should return None.

For instance, if you have the following conversions: ("USD", "EUR", 0.88), ("EUR", "JPY", 129.53), and ("GBP", "USD", 1.39), the algorithm should be able to deduce the conversion rate from "USD" to "JPY" as well as from "GBP" to "EUR".

Examples:

conversions = [
    ('USD', 'EUR', 0.88),
    ('EUR', 'JPY', 129.53),
    ('GBP', 'USD', 1.39)
]

source = 'USD'
destination = 'JPY'
output: 114.0064  # 0.88 * 129.53

source = 'GBP'
destination = 'EUR'
output: 1.2232  # 1.39 / 0.88

source = 'EUR'
destination = 'GBP'
output: None  # No direct or indirect conversion available

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