Stella and Twinkle are filling up a truck with a capacity of 6000 stone blocks at the rate of 250 blocks per hour per person. They work for four hours and are then joined by 6 other people who also work at the same rate. How many hours did filling the truck take?
Stella and Twinkle filled up the truck at the rate of 250 blocks per hour per person, a total of 2*250 = <<250*2=500>>500 blocks per hour for both.
After working for four hours, Stella and Twinkle had filled 4*500 = <<4*500=2000>>2000 blocks into the truck.
The number of blocks they had to put into the truck for it to be full is 6000-2000 = <<6000-2000=4000>>4000
When 6 more people joined Stella and Twinkle, a total of 2+6 = <<2+6=8>>8 people were filling the truck now.
Working at the rate of 250 blocks per person, the eight people filled the truck with 250*8 = <<250*8=2000>>2000 blocks in one hour.
If there were 4000 blocks that still needed to be put into the truck, the 8 people took 4000/2000 = <<4000/2000=2>>2 hours to fill the truck with the blocks.
The total time it took to fill up the tank is 4+2 = <<4+2=6>>6 hours.
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