On her breakfast tray, Aunt Lily had a little vase of flowers--a mixture of primroses and celandines. She counted up the petals and found there were 39. "Oh, how lovely!" she said, "exactly my age; and the total number of flowers is exactly your age, Rose!"
How old is Rose?
Primroses have five petals on each flower.
Celandines have eight petals on each flower.. 作者: dayan888 时间: 2007-10-4 20:00
On her breakfast tray, Aunt Lily had a little vase of flowers--a mixture of primroses and celandines. She counted up the petals and found there were 39. "Oh, how lovely!" she said, "exactly my age; and the total number of flowers is exactly your age, Rose!"
How old is Rose?
Primroses have five petals on each flower.
Celandines have eight petals on each flower.
The way to figure this out is to start at the end with 39 petals. and remember that the primroses must provide either 5 petals or 10 or 15 or 20 or 30-a multiple of 5. Now suppose there was only one celandine (8 petals); that would leave 31 petals (39-8=31). The rest can't be primroses, because 31 is not an exact multiple of 5. Suppose there were two celandines; that would make 16 petals, leaving 23. No good! Three celandines=24 petals, and 39-24=15 petals. Bingo! The answer must be 3 celandines and 3 primroses. Check: 3x8=24 and 3x5=15, and 24+15=39. So Rose is (3+3), or 6.
Is this clear enough?
又学英语又学数学。. 作者: clairez 时间: 2007-10-6 17:46
I really taste it as it reminded me of my college life as our maths, physics and chemistry were delivered in English at that time! Mechanical drawing and EE were taught in English also. But unfortunately I forgot most of the staff taught then. Claire. 作者: H爸 时间: 2007-10-6 18:08
Sue invited 4 friends to go with her to the movies;There are 120 different ways in which they can sit together in a row.In how many of those ways is Sue siting in the middle?. 作者: chrisabs 时间: 2009-6-22 22:24
尽管不大懂。
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