plz answer these questions with reasons

If 1 inch = 2.54 centimeters, centimeter equals which of the following in inches?


.One number is 5 times another number and their sum is -60. What is lesser of the two numbers?


The average of x numbers is 15. If two of the numbers are each increased by y, the new average will be increased by how much?


.A fair coin is tossed three times. What is the probability that at least one head appears?


.A square and an equilateral triangle have the same perimeter. The area of the square is 225 cm. What is the length of a side of the triangle?