How long can the average 13 year old focus?

If velocity is measured in kilometers per hour and time is measured in hours the unit of acceleration is? How do you read 0.205 in words? What is the circumference of a circle with a radius of 4.5 centimeters? How many natural numbers below 1000 can be written as difference of squares of two natural numbers? Find the sum of fifteen hundredths and seven tenths? What are two consecutive odd integers that have a sum of 130? What is one minus negative 2? What is 11in binary? What goes equally into 15? How do you write 25500? What is the slope and what is the y intercept of y equals mx plus b? What is the roman numeral for 1809? What is the LCM of 132 144 156? What is SecNet 54? How do you round 31 to the nearest hundred? How do you write 80000003009 in standard form? What is 20 percent of 386? What is 18.225 fractional notation? How do you do the sum 14.5 by 24? What happens to Tzipporah in the Devils Arithmetic?