Question

Maria can stack a pile of wood in 20 minutes, and

alex can stack the same pile of wood in 12 minutes.
how long will it take them both working together
to stack the same pile of wood?

Answer 1

7.5 minutes

Explanation:

The stacking rate working together is assumed to be the sum of the separate stacking rates. The rates are given in terms of minutes per pile, but we need to do the computation with rates in terms of piles per minute.

__

total rate = Maria's rate + Alex's rate

= 1/20 piles/min + 1/12 piles/min = (12 +20)/(20·12) piles/min

= 32/240 piles/min = 2/15 piles/min

Then the rate in terms of minutes per pile is ...

1/(2/15 piles/min) = 15/2 min/pile = 7.5 min/pile

When both work together, it will take them 7.5 minutes to stack a pile of wood.