The urn contains 7 red and 4 blue balls.
Total number of balls in the bag = 7 + 4 = 11
Two balls are drawn at random from the bag with replacement.
We know that:
Probability of an event E =number of outcomes favourable to event E/total outcome
P(Getting one red ball)=7C1/11C1=7/11
P(Getting one blue ball) =4C1/11C1=4/11
P(Getting 2 red balls) =7/11 *7/11=49/121
P(Getting 2 blue balls) =4/11*4/11=16/121
P(Getting one red and one blue ball)=7/11*4/11=28/121