Un deportista de atletismo de alto rendimiento pudo determinar que por cada día de entrenamiento disminuye un segundo en su registro personal. Su marca actual es de 9 minutos. Para poder participar en los Juegos Olímpicos de Brasil 2016, requiere bajar su registro a los dos tercios de su marca actual. ¿Cuántos días requiere entrenar para poder participar en los Juegos Olímpicos de Brasil 2016?
a. 360 días
b. 120 días
c. 60 dias
d. 180 días

the largest number of the four options is 1.8 x 10-2

you have it in scientific notation.

1.80 x 10-6   = 0.00000180

1.80 x 10-4   = 0.000180 (bigger, or "less small", than the former one)

so

1.8 x 10-2       = 0.0180. as you see. the "less small", or the biggest one of them all.

as you have negative exponent, it means you are dividing 1.8 by 100 (i.e. moving the dot towards left, two times).

if you had positive exponent for the scientific notation, power of tenths, you would be multiplying times 100 (moving the dot towards right) as below:

1.8 x (10)2 = 180

so. if you have negative exponent in scientific notation, move the dot toward left. if it is positive, toward right as many times the exponent tells you.

this would be 35. 35 + 5 = 40. you take the known constant and subtract by the answer of the equation and you get y.