Fred is playing the slot machines. after a certain number of plays, he wins a few coins, but fred is unable to determine how many plays he needs to win. which of the following statements is true? a. fred is on a fixed-interval schedule of reinforcement. b. fred is on a variable-interval schedule of reinforcement. c. fred is on a fixed-ratio schedule of reinforcement. d. fred is on a variable-ratio schedule of reinforcement.

Asheet of steel 1.5 mm thick has nitrogen atmospheres on both sides at 1200oc and is permitted to achieve a steady-state diffusion condition. the diffusion coefficient for nitrogen in steel at this temperature is 6 x 10- 11 m2 /s, and the diffusion flux is found to be 1.2 x 10-7 kg/m2 -s. also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m3 . how far into the sheet from this high-pressure side will the concentration be 2.0 kg/m3 ? assume a linear concentration profile.

Jenny wants to test the electrical conductivity of two substances dissolved in water. she is preparing the containers for the experiment. which factor is most important for her to control? a) volumes of the solutions b) appearance of the solutions c) temperatures of the solutions d) concentrations of the solutions

An electron in an x-ray machine is accelerated through a potential difference of 1.00 × 104 v before it hits the target. what is the kinetic energy of the electron in electron volts?