In Macroland, currency held by the public is 2,000 econs, bank reserves are 300 econs, and the desired reserve/deposit ratio is 10 percent. If the Central Bank prints an additional 200 econs and uses this new currency to buy government bonds from the public, the money supply in Macroland will increase from econs to econs, assuming that the public does not wish to change the amount of currency it holds.

the money supply in Macroland will increase from 5,000 econs to 7,000 econs

Explanation:

Currently, Macroland's money supply = 2,000 econs held by the public and 3,000 econs held by the banks (= 300 econs x 1/0.1).

In order to determine the increase in the money supply we must multiply the inflow of econs by the money multiplier. The money multiplier = 1 / reserve ratio = 1/0.1 = 10.

Since the government is injecting 200 econs to the economy, the increase in the money supply = 200 econs x 10 = 2,000 econs.

So now, Macroland's money supply will increase from 5,000 to 7,000 econs.

The money multiplier measures the banking system's ability to "create" money. The banking system creates money by first receiving deposits, e.g. you deposit 10 econs in your savings account, and then lending money to another client. The bank will lend 9 econs (-10% required reserve) to John that will purchase a bike. The seller of the bike receives the money form John and deposits the 9 econs in his own bank. Then this second bank will lend 8.10 econs to Sarah. Sarah will use the money to purchase a new computer and a printer from Tom. Tom then deposits the money in his bank, and then his bank lends 7.29 econs to Sally, and the wheel goes on and on.

This money creating process is possible because Macroland uses a fractional banking system, which means that the banks are only required to keep a fraction of total deposits as reserves.