Question 436169
Nita	90	minutes				
she does	  1/90	of the job in 1 	minute			
pedro	60	minutes				
he does	  1/60	of thejob in 1 	minute			
Together they will do   1/90+ 1/60	
Together they will do   1/36 of the job in one 	minute

in 10 minutes Nita does 10*1/90 of the job
=1/9 of the job.
Balance remaining when pedro joins = 1-1/9 = 8/9 of the job.

they do 1/36 of the job in 1 minute
for 8/9 of the job they will take
(8/9)/(1/36)
8/9*36/1
=32 minutes
=32 minutes to mow the lawn.