In the figure, AD and BC are lines intersecting at O. What is the value of a?

There are 3 green, 4 orange and 5 white colour bulbs in a bag. If a bulb is picked at random, what is the probability of having either a green green or a white bulb?

In a class 75% passed in English, 60% in Mathematics and 25% failed in both the subjects. What is the percentage who passed in both subjects?

The speed of three cars is in the ratio of 2 : 3 : 4 . The ratio of the times taken by these cars to travel the same distance is -

At what profit percent must an article be sold so that by selling at half that price, there will be a loss of 30%?