7. Two bells ring at an interval of 30 minutes and 40 minutes to change the lessons in lower and upper primary respectively,
a) After how long will they ring together at the same time?
b) If they first ring together at 9:15 a. m. at what time will they ring together again?​

a: 45.9 meters

b: 4.29 seconds

step-by-step explanation:

a: h(t)=1/2(-9.8)(3)^2+0(3)+90

h(t)=-4.9(3)^2+90

h(t)=-44.1+90

h(t)=45.9 meters

b: 0=1/2(-9.8)(t^2)+0t+90

0=-4.9t^2+90

-90=-4.9t^2

18.37=t^2

t=4.29 seconds

in the second question, the numbers aren't exact, but they're a close approximation.

water and alcohols have similar properties because water molecules contain hydroxyl groups that can form hydrogen bonds with other water molecules and with alcohol molecules, and likewise alcohol molecules can form hydrogen bonds with other alcohol molecules as well as with water.

metric time was an attempt to create a standard unit of time based off of 10, but it never took off an is not included in the metric system (si)