7x10^15 grains of sand in world

Twice the sum of a number and 4 is equal to three times the difference of the number and 7. find the number.

An office supply company conducted a survey before marketing a new paper shredder designed for home use. in the survey, 80 % of the people who tried the shredder were satisfied with it. because of this high satisfaction rate, the company decided to market the new shredder. assume that 80 % of all people are satisfied with this shredder. during a certain month, 100 customers bought this shredder. find the probability that of these 100 customers, the number who are satisfied is 69 or fewer.

Find the area of the region that is inside r=3cos(theta) and outside r=2-cos(theta). sketch the curves.