In a primary school, the parents were asked the number of hours they spend per day in helping their children to do homework. There were 90 parents who helped hour to hours. The distribution of parents according to the time for which they said they helped is given in the adjoining figure; 20% helped for more than hours; 30% helped for hour to hours; 50% did not help at all.
Using this, answer the following :
(i) How many parents were surveyed?