A speaks truth in 70% cases and B in 80% cases. What will be the probability that they will contradict each other in describing a single event?

Annual increase in population of a city is 4% and the present population is 40000. What will be the population of the city after 2 years?

If the cost price of a Mobile is first decreased by 25% and then increased by 20%. What will be the net change in the prices?