The money supply will increase only if high-powered money is injected by the RBI into the economy, right? Then how come credit is created by commercial banks merely by lending funds for investment/consumption? 

Dear student,

High powered money includes currency notes and coins held by public and commercial banks, deposits held by government and commercial bank with Central Bank. The RBI by injecting high powered money ​increase supply of money but the money is not available to all public for investment purpose therefore, commercial banks increase the flow of money by creation of credit and accepatnce of deposits.

Regards