Using the digits 0-9, how many numbers can be configured is the number cannot start with 0

The? half-life of a radioactive substance is 20 years. if you start with some amount of this? substance, what fraction will remain in 120 ? years

The figure shows triangle def and line segment bc, which is parallel to ef: triangle def has a point b on side de and point c on side df. the line bc is parallel to the line ef. part a: is triangle def similar to triangle dbc? explain using what you know about triangle similarity. part b: which line segment on triangle dbc corresponds to line segment ef? explain your answer. part c: which angle on triangle dbc corresponds to angle f? explain your answer. asap

Order the equations from least to greatest based on the number of solutions to each equation.-4^x -1 = 3^(-x) – 2 -3x + 6 = 2^x+13^x – 3 = 2x - 2