What does a circle with an x through it mean?

Where did people use Egyptian numerals? What goes into 24 and 60? What is 2 over 4 equal? Are one- or two-floor lodging establishments in which the rooms are usually accessible from an outdoor parking area? Why will a toy car stop when you push it? Why is there a 2 in each part of the surface area formula for a rectangular prism? What is the outputor y-valuewhen you input x-4 into the function y2x plus 6? Is 9.42 a rational number? What is x in the equation -3x squared minus 5x plus 12 equals 0? What is x in 20x equals 140? What is plywood? What two number add to give you 7 and multiply to give you 18? How do you know what the base of a triangle is? What is 10 percent of 35 pounds? Statistics.When a given point under the normal curve is 1.54 standard deviation units above the mean then ait's is 15.4 bit's is 1.54 cit's z score is 1.54 dboth a and c but not b? 130 percent of 600 is what? What are all of the prime numbers from 51-100? What is 1600 plus 81? How many gallons of gas does it take to drive 103 miles? What is the formula called a equals b b equals c therefore a equals c?