The number of ways of placing 3 black balls without any restriction is 10C3​. Since, we have total 10 places of putting 10 balls in a row. Now, the number of ways in which no two black balls put together is equal to the number of ways of choosing 3 places marked '-' out of eight places.−W−W−W−W−W−W−W−This can be done in 8C3​ ways.∴ Required probability =10C3​8C3​​=10×9×88×7×6​=157​