✔ 最佳答案
1) the sum of ascending numbers is easy. Just remember the rule
(1st number + last number) x n / 2
--> n is the number of integers. So for 1 - 82, there are 82 numbers. n = 82.
Therefore, for this question, ANSWER is:
(1 + 82) * 82 / 2 = 3043
2) This is little tricky. I will try to explain.
2007 * n = xxxx837->we don't know how many "x" and we don't need to care
以7的倍數來看, n 的尾數(last digit)一定會是1
So, n = xxx1
2007
* x1
-----
xxx7
跟住,n的第二尾數會是9
因為只有*9先可以有3在尾
2007
* x91
-----
x630
+2007
-----
x637
跟住,n的第三尾數會是6!
因為只有*6先可以有2在尾
咁2+6就有8在answer的第三尾
2007
* 691
-----
4200
+x630
-----
x830
+2007
-----
x837
3) This is a gernal physics question
You just need to know:
velocity = distance / time
(v = d / t)
d = 隧道長度
v = 貨櫃車速
t = 穿過隧道時間
原本
v = (d + 6) / t
第二天,
0.8v = (d + 12) / 1.5t
0.8v -> 車速調低20%
1.5t -> 需時增加了一半
simutaneous equations to solve for d:
d = 24m
4) I do not understand what you are asking for this question, sorry!
數字共會出現多少次 --> not understand..
