又有数学问题要请教大家了~~嘻嘻

self346959851

81.If each term in the sum a1 + a2 + . . . + an is either 7 or 77 and the sum equals 350, which of the following could be equal to n ?

题目意思不懂。。。

131.  If the speed of x meters per second is equivalent to the speed of y kilometers per hour, what is y in terms of x ?
答案18x/5

141.14419-!-item-!-187;#058&009981

If (5^21)(4^11) = 2(10^n) what is the value of n ?

答案
(B) 21



另外，扎道题的中文神马意思？
Alice's take-home pay last year was the same each month, and she saved the same fraction of her take-home pay each month.The total amount of money that she had saved at the end of the year was 3 times the amount of that portion of her monthly take-home pay that she did not save.If all the money that she saved last year was from her take-home pay, what fraction of her take-home pay did she save each month?

lestatwm

81.If each term in the sum a1 + a2 + . . . + an is either 7 or 77 and the sum equals 350, which of the following could be equal to n ?

题目意思不懂。。。

在算式a1 + a2 + . . . + an中, 所有元素或者是7, 或者是77, 并且该算式的总和为350, n可能等于以下哪个数字?

N个数的和为350, 这些数的可能只有两种: 7 或 77.
由350/77可知: 最多可能有4个77, 350-4X77=42, 42/7=6, 所以N=4+6=10
当有3个77时, 350-3X77=119, 119/7=19, 所以N=3+19=22
当有2个77时, 350-2X77=196, 196/7=28, 所以N=2+28=30
当有1个77时, 350-77=273, 273/7=39, 所以N=1+39=40

131.  If the speed of x meters per second is equivalent to the speed of y kilometers per hour, what is y in terms of x ?
答案18x/5

X=1000Y/3600
得出Y=18X/5

141.14419-!-item-!-187;#058&009981
没明白是什么意思

If (5^21)(4^11) = 2(10^n) what is the value of n ?

答案
(B) 21

看上去很累, 其实原理很简单X^n)(Y^n)=(XY)^n

(5^21)(4^11)=(5^10)[(5^11)(4^11)]=(5^10)(20^11)=[(5^10)(20^10)](20)=20(100^10)=20(10^20)=2(10^21)


另外，扎道题的中文神马意思？
Alice's take-home pay last year was the same each month, and she saved the same fraction of her take-home pay each month.The total amount of money that she had saved at the end of the year was 3 times the amount of that portion of her monthly take-home pay that she did not save.If all the money that she saved last year was from her take-home pay, what fraction of her take-home pay did she save each month?

这道题我在做PREP时也遇到了, 把我也绕晕了，其实非常简单， 一元一次方程可以解决的问题， 说得太复杂了。

Alice每个月的月薪数目相同， 她每个月都要从月薪中取出固定的一部分用于储蓄，年底时她的储蓄总数是她每月月薪中非储蓄部分的3倍，如果她去年所有储蓄都来自于他的月薪，那么她每个月储蓄占月薪的比例是多少？

设Alice月薪为A，每月存钱数为a，方程就是12a/(A-a)=3, 得出a/A=1/5

self346959851

81.If each term in the sum a1 + a2 + . . . + an is either 7 or 77 and the sum equals 350, which of the following could be equal to n ?

题目意思不懂。。。

在算式a1 + a2 + . . . + an中, 所有元素或者是7, 或者是77, 并且该算式的总和为350, n可能等于以下哪个数字?

N个数的和为350, 这些数的可能只有两种: 7 或 77.
由350/77可知: 最多可能有4个77, 350-4X77=42, 42/7=6, 所以N=4+6=10
当有3个77时, 350-3X77=119, 119/7=19, 所以N=3+19=22
当有2个77时, 350-2X77=196, 196/7=28, 所以N=2+28=30
当有1个77时, 350-77=273, 273/7=39, 所以N=1+39=40

131.  If the speed of x meters per second is equivalent to the speed of y kilometers per hour, what is y in terms of x ?
答案18x/5

X=1000Y/3600
得出Y=18X/5

141.14419-!-item-!-187;#058&009981
没明白是什么意思

If (5^21)(4^11) = 2(10^n) what is the value of n ?

答案
(B) 21

看上去很累, 其实原理很简单X^n)(Y^n)=(XY)^n

(5^21)(4^11)=(5^10)[(5^11)(4^11)]=(5^10)(20^11)=[(5^10)(20^10)](20)=20(100^10)=20(10^20)=2(10^21)


另外，扎道题的中文神马意思？
Alice's take-home pay last year was the same each month, and she saved the same fraction of her take-home pay each month.The total amount of money that she had saved at the end of the year was 3 times the amount of that portion of her monthly take-home pay that she did not save.If all the money that she saved last year was from her take-home pay, what fraction of her take-home pay did she save each month?

这道题我在做PREP时也遇到了, 把我也绕晕了，其实非常简单， 一元一次方程可以解决的问题， 说得太复杂了。

Alice每个月的月薪数目相同， 她每个月都要从月薪中取出固定的一部分用于储蓄，年底时她的储蓄总数是她每月月薪中非储蓄部分的3倍，如果她去年所有储蓄都来自于他的月薪，那么她每个月储蓄占月薪的比例是多少？

设Alice月薪为A，每月存钱数为a，方程就是12a/(A-a)=3, 得出a/A=1/5

-- by 会员 lestatwm (2011/3/28 22:57:43)

额。。。我把这道题理解成她每月存钱副回家路费，然后没存的又怎么怎么了。。。
半天没明白什么意思。。。

本人理解能力太差了 哎

谢谢啦~我都明白了。 说的非常详细~~