Question

In a primary school , the parents were asked about the number of hours they spend per day in helping their chaildren do their homework . there were 90 parents who helped for 1 and a half or half hour.50% did not help , 20% helped more 1 and a half hour and 30% helped for half hour to 1 and half hour .
how many parents were surveyed ?
how many said they did not help ?
how many said they did not helped for more than 1 and a half ?

Answer 1

Let the number of surveyed parents equals $N$. Then we have equation:

$$0.3N = 90$$ $$N = \frac{90}{0.3} = 300$$

So 300 parents were surveyed.

$N \cdot 0.5 = 300 \cdot 0.5 = 150$ parents said they did not help.

$N - N \cdot 0.2 = 300 - 300 \cdot 0.2 = 240$ parents said they did not help for more than 1 and half.