Mr. mcgregor has discovered that a large dog can destroy his entire garden in 2 hours and that a small boy can do the same job in 1 hour. how long would it take the large dog and the small boy working together to destroy mr mcgregor's garden?

For the rule of 78, for a 12-month period, the last term in the sequence is 12 and the series sums to 78. for an 10 month period, the last term is and the series sum is . for a 15 month period, the last term is and the series sum is . for a 20 month period, the last term is and the series sum is