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Meaning of letters and symbols: 
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K 
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is the number of a loan 
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K′ 
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is the number of a repayment or a payment of charges 
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AK 
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is the amount of loan number K 
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A′K′ 
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is the amount of repayment number K′ 
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represents a sum 
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m 
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is the number of the last loan 
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m′ 
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is the number of the last repayment or payment of charges 
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tK 
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is the interval, expressed in years and fractions of a year, between the date of loan No. 1 and those of subsequent loans Nos. 2 to m′ 
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tK′ 
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is the interval expressed in years and fractions of a year between the date of loan No. 1 and those of repayments or payments of charges Nos. 1 to m1 
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i 
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is the percentage rate that can be calculated (either by algebra, by successive approximations, or by a computer programme) where the other terms in the equation are known from the contract or otherwise. 
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