Bob can stamp all envelopes in the office in 5 hours and John can do the same job in 7 hours. How long will it take two of them to do this job?

Bob and John can finish the job together in approximately 2.92 hours or 2 hours and 55 minutes

Step-by-step explanation:

Let's recall that the formula for solving this kind of problems is:

T/A + T/B = 1, where T = time working together, A = the time for person A working alone, and B = the time for person B working alone.

Now, replacing with the values we have:

T/5 + T/7 = 1

35 is the Lowest Common Multiple of 5 and 7

5T + 7T = 35

12T = 35

T = 35/12

T = 2.92 (Rounding to the next hundredth) and 0.92 * 60 ≅ 55

T ≅ 2.92 hours (Around 2 two hours and 55 minutes)