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?​

The diagram below shows the different phase transitions that occur in matter. which arrow represents the transition in which dew is formed?

12. calculate the hydroxide ion concentration of a solution with ph = 3.25. show all calculations leading to an answer

13. a covalent bond between two atoms is likely to be polar if: a. one of the atoms is much more electronegative than the other. b. the two atoms are equally electronegative. c. the two atoms are of the same element. d. the bond is part of a tetrahedrally shaped molecule. e. one atom is an anion.