"How can national investment be linked to national savings?" National investment is matched with national savings through the financial market-this is actually the definition of financial market and its function. For example, if you deposit money in a bank, it is savings, and then the bank lends this money to others for investment, and the two are linked.

"How can we ensure that savings must be equal to investment?" In the loanable funds market, demand comes from investment and supply comes from savings, so when the market reaches equilibrium, savings = = investment.

"If I save half of my money and invest the other half myself, that part of my investment also belongs to national investment." In macroeconomics, investment is a proper term, which means "the purchase of machinery and related buildings used in production, that is, the production of machinery and buildings is not directly consumed, but used as production factors to expand production." What you mean by "investment" is our usual meaning, for example.

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