algebra
posted by sandra .
it john 4 hours to mow a lawn it takes maria 3 hours to mow the same lawn, how long would it take if they worked together?

well, if they mowed for 12 hours, they would cut 3+4=7 lawns.
rate=7lawns/12 hours
1lawn=rate*time=7/12 lawns/hr*time
time= 12/7 hrs or 1 5/7 hr 
John mows lawn in 4 hrs or .25 lawn in 1 hr. Maria mows lawn in 3 hrs or .333 lawn in 1 hr. So in one hour they (combined) mow .25 + .333= .583 lawn(assuming they don't remow each others sections, lol)
1/.583 is 1.715hr
John should just go home and let maria do it all.
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