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## Economic Assumptions 

The most significant economic assumptions made in the measurement of the pension costs and the projected benefit obligations of the pension plans and OPEB were as follows: 

<img src='content_image/121844.jpg'>

A 1% change in the assumed medical and dental care trend rate would result in a $17.4 million change in the accumulated post-employment benefit obligations and a $2.0 million change in post-employment benefit costs. 

## 12. Investment and Other Income 

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The reduction in federal and provincial income tax rates has resulted in certain of the Company’s anticipated U.S. dollar cash flows being overhedged. The derivative financial instruments related to the overhedged position, primarily long-term forward foreign exchange contracts, have been treated as speculative and marked to market, resulting in a charge of $24.5 million to earnings. 

## 13. Changes in Operating Assets and Liabilities 

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Changes in accounts payable exclude changes in construction payables which relate to investing activities. 

