數學問題(快) 20點

為方便解答這2條問題 我會先舉出所有可能性再剔除不對的答案

## 3. 答案: 1080cm

小光每步長54cm:
54 108 162 (216) 270 324 378 (432) 486 540 594 (648) 702 756 810 (864) 918 972 1026 (1080)...

爸爸每步長72cm:
72 144 216 288 360 432 504 576 648 720 792 864 936 1008 1080...

當你由小至大順序排列(剔除重覆的答案) 數至第30個位置(60個腳印)就是你需要的答案(即1080cm)


## 4. 答案: 188人

這題目可以用類似的方法排列出可能性 (或解 5x+3=9y+8=7z+6)
因為5的倍數個位數一定是5或0 所以5x+3的個位一定是3或8
再列出9y+8的數序:
8 17 26 35 44 53 62 71 80 89 98 107 116 125 134 143 152 161 170 179 188 197...

只有 8 53 98 143 188 符合以上2個條件
而只有188才符合所有3個條件

3) 2160cm ( 54同72既最小公倍數係 216 , 而216米裏( 已計重合 )有6個腳印 , 60/6 = 10 , 216 x 10 = 2160 )

4) 188人 ( 每5人多3人 , 即該數的個位一定係3或8 , 然後慢慢試啦.....= = )

3. 答案: 1080cm

4. 答案: 188人

第3: 小光54,108,162,216,270,324,378,432,486,540,594,648,702,
756,810,864,918,972,1026,1080,1134,1188,1242,1296,1350,
1404,1458,1512,1566,1620,1674,1728,1782,1836,1890,1944,
1998,2052,2106,2160,2214,2268,2322,2376...
爸爸
72,144,216,288,360,432,504,576,648,720,792,864,936,
1008,1080,1152,1224,1296,1368,1440,1512,1584,1656,1728,
1800,1872,1944,2016,2088,2160,2232,2304,2376...
合
54,72,108,144,162,216,270,288,324,360,378,432,486,504,
540,576,594,648,702,720,756,792,810,864,918,936,972,1008,
1080,1134,1152,1188,1224,1242,1296,1350(36),1368,1404,
1440,1458,1512,1566,1584,1620,1656,1674,1728,1782,1800,
1836,(50)1872,1890,1944,1998,2016,2088,2052,2106,2160,
2214(60)

2214

第4題
住房:8(5+3),13,18,23,28,33,38,43,48,53,58,63,68,73,78,
83,88,93,98,103,108,113,118,123,128,133,138,143,148,153,
158,163,168,173,178,183,(188),193,198

吃飯:8(9-1),17,26,35,44,53,62,71,80,89,98,107,116,125,
134,143,152,161,170,179,(188),197

開小組:13(7=6),20,27,34,41,48,55,62,69,76,83,90,97,
104,111,118,125,132,139,146,153,160,167,174,181,(188),
195
188

用大角嘴天主教小學(海帆道)的數學能力自我挑戰(五年級）
來問人..

3 , 720cm
4, 唔識