Division using multiples of 10 is different than how most of us learned how to divide. <span>The idea of multiple is what number can 10 go into without a remainder. That is easy. Ten ends in a zero. Thus 10 goes into numbers ending in zero. An example is 60. Ten ends in a zero; 60 ends in a zero. It will divide evenly. </span>
The formula is time = (Worker 1 * Worker 2) / (Worker 1 + Worker 2) time = (18 * 20) / (18 + 20) time = 360 / 38 time =
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9.4736842105
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minutes So, the answer is "a. 9.5 minutes".
