gpsm

I can't figure these out =( Can anyone help?!

Sheila can wash her car in 15 minutes. It takes Bob twice as long to wash the same car. How long does it take them to wash the car working together?

A container is partially filled with 12 liters of whole milk containing 4% butterfat. How much 1% milk must be added to get a mixture that is 2% butterfat? Construct a table, then solve.

An 80-pound grass seed mixture is 30% bluegrass seed. How many pounds of seed containing no bluegrass seed (0%) should be added to the seed mixture for a resulting blend that is 20% bluegrass seed? Construct a table, then solve.

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Answer:1. 10 minutes (Sheila does 2/3 of the car in 10 minutes and Bob does 1/3 of the car in 10 minutes)

2. 24 liters ((24*1% 12*4%)/36=2%)

3. 40 pounds ((80*30% 40*0%)/120=20%)

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