Twin brothers, person a and person b, can mow their grandparent's lawn together in 18 minutes. person a could mow the lawn by himself in 15 minutes less time than it would take person
b. how long would it take person b to mow the lawn by himself?

3x + 4y = 5 x- 3y = -7 solve by substitution

What is the missing reason in the proof? segment addition congruent segments theorem transitive property of equality subtraction property of equality?

For every corresponding pair of cross sections, the area of the cross section of a sphere with radius r is equal to the area of the cross section of a cylinder with radius and height 2r minus the volume of two cones, each with a radius and height of r. a cross section of the sphere is and a cross section of the cylinder minus the cones, taken parallel to the base of cylinder, is the volume of the cylinder with radius r and height 2r is and the volume of each cone with radius r and height r is 1/3 pie r^3. so the volume of the cylinder minus the two cones is therefore, the volume of the cylinder is 4/3pie r^3 by cavalieri's principle. (fill in options are: r/2- r- 2r- an annulus- a circle -1/3pier^3- 2/3pier^3- 4/3pier^3- 5/3pier^3- 2pier^3- 4pier^3)