1 answer
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work=rate*time
worktotal=sallyrate*time + johnrate*time
time= worktotal/(sallyrate +johnrate)
= 1house/(house/4 + house/6)
= 24/24 * 1/(1/4 + 1/6)
= 24 * 1/(6 + 4)= 24/10 hrs
check my thinking.