下列哪一組數的 L.C.M. 是90 而 H.C.F. 是15?
Which of the following sets of numbers has 90 as their L.C.M. and 15 as their H.C.F. ?
A. 2x2x3 , 2x3x5
B. 2x3x5 , 3x3x5
C. 2x3x3 , 3x3x5
D. 2x2x5 , 3x3x5
我知到個答案,但係點解佢要寫2x2x3而唔寫12呢??
Mathematics
2007-12-26 7:24 pm
回答 (3)
2007-12-26 7:45 pm
✔ 最佳答案
因為咁寫 係幫你計...點講好...
比個eg你
好似 A咁
第一個:２ｘ２ｘ３
第二個:２ ｘ３ｘ５
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lcm: ２ｘ２ｘ３ｘ５＝６０
hcf: ２ ｘ３ ＝６
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check一次
2x2x3=12
2x3x5=30
hcf真係6
lcm都係60
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其實就係lcm有幾多拎幾多..
hcf就係2個都有先拎..
好似我上面咁寫..就好清楚
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ans 係b la 應該..我心算..唔知有無算錯~~
參考: 自己~~
2007-12-30 8:45 pm
係點解佢要寫2x2x3而唔寫12呢?
because we want to get L.C.M and H.C.F, we need to factorise every number
2x2x3 = 12, but write down 2x2x3, you don't need to factorise 12
L.C.m is 90 = 2x3x3x5, and H.C.F is 15 = 3x5
so
2 can not be exist in both numbers of sets, A rejected
3x3 can not be exist in both numbers of sets, C rejected
3x5 must be exists in both numbers of sets, D rejected
hence, the answer is B
because we want to get L.C.M and H.C.F, we need to factorise every number
2x2x3 = 12, but write down 2x2x3, you don't need to factorise 12
L.C.m is 90 = 2x3x3x5, and H.C.F is 15 = 3x5
so
2 can not be exist in both numbers of sets, A rejected
3x3 can not be exist in both numbers of sets, C rejected
3x5 must be exists in both numbers of sets, D rejected
hence, the answer is B
參考: 自己
收錄日期: 2021-04-23 17:34:28
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