Explain the problem of 'double coincidence of wants faced under barter system

Explain the problem of 'double coincidence of wants faced under barter system. How has money solved it?

Double coincidence of wants Barter system can only work, when both the persons are ready to exchange each other’s goods. But usually this type of double coincidence is rare to find.
Money eliminates the problem of double coincidence of wants as, the buyer and seller both exchange goods or services for money. It facilitates exchanges of goods , and services and helps in carrying on trade smoothly.