Next to a straight runway, 51 flags were planted, with an interval of 2 meters. Later, only 26 small flags were planted, with an average interval of how many meters? (both ends are inserted)

Next to a straight runway, 51 flags were planted, with an interval of 2 meters. Later, only 26 small flags were planted, with an average interval of how many meters? (both ends are inserted)

A: the average interval is 4 meters

1. Peng louting clock every time the sound lasts for 3 seconds, 8 times, a total of 73 seconds. So how many seconds does it take to ring 13 times?
2. It took 160 seconds for Xiaoyu to reach the third floor and 240 seconds for Xiaohao to reach the fifth floor. When Xiaoyu reached the seventh floor, which floor was Xiaohao on?
3. Brother and sister climb a hillside with 330 steps together. Brother steps up three steps, sister steps up two steps. Q: how many steps did brother and sister step from the starting point to the end of the hillside

(1) 13 * 3 + 12 * 7 = 123 (seconds), 8 rings, indicating that the interval between each segment (a segment of 3 seconds) is a total of 7 segments, and the duration is (73-8 * 3) / 7 = 7 (seconds); 13 times, the interval between 12 segments is 13 * 3 + 12 * 7 = 123 (seconds)
(2) 6 * 80 / 60 + 1 = 9 (floor), it takes two floors to reach the third floor and four floors to reach the fifth floor. It takes 80 seconds for Xiaoyu to reach each floor and 60 seconds for Xiaohao. It takes 480 seconds for Xiaoyu to reach the seventh floor. Xiaohao is at 6 * 80 / 60 + 1 = 9 (floor)
(3) Brother steps up three steps, sister steps up two steps. That is to say, in every six steps, two people step on four steps (you can see from the picture below). There are 330 steps, with a total of 330 / 6 = 55 cycles, with a total of 55 * 4 = 220 steps

20 problems of formulaic calculation in grade 4 of primary school

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