Final answer:
The approximate number of heartbeats for all the people in the world per year is 3.192 x 10^17.
Step-by-step explanation:
To approximate the number of heartbeats for all the people in the world per year, we first need to calculate the total number of heartbeats per year for one person. Given that the average heart beats about 4.2 x 10^7 times per year, we can multiply this by the total number of people in the world (7,600,000,000), resulting in approximately 3.192 x 10^17 heartbeats per year for all the people in the world. Therefore, the values of a and b in scientific notation are 3.192 x 10^17.