Simple algorithm 4000-1-2-3 -... - 77-78 Simple calculation 5.48 - (9.4-0.52) Simple calculation 3.65x10.14.8x100.1

Simple algorithm 4000-1-2-3 -... - 77-78 Simple calculation 5.48 - (9.4-0.52) Simple calculation 3.65x10.14.8x100.1

4000-1-2-3 -... - 77-78 = 4000 - (1 + 2 + 3 +... + 77 + 78) = 4000-78 * (78 + 1) / 2 = 4000-3081 = 919 simple calculation 5.48 - (9.4-0.52) = 5.48-9.4 + 0.52 = 6-9.4 = - 3.4 simple calculation 3.65x10.1 = 3.65x (10 + 0.1) = 36.5 + 0.365 = 36.8654.8x100.1 = 4.8x (100 + 0.1) = 480 + 0

What is 39 / 5 / [32 * (1-5 / 8) + 18 / 5] + 1?

39/5/【32*(1-5/8)+18/5】+1
=39/5/【32*3/8+3.6】+1
=39/5/【12+3.6】+1
=39/5/15.6+1
=39/78+1
=1/2+1
=3/2
one point five

36x (2 / 9 + 7 / 12)
Write the process

36*(2/9+7/12）
=36*2/9 + 36*7/12
=8+21
=29

5 / 12 × 7 / 13 × 36
How to simplify and calculate

=（5/12）*7（/13）*36
=（5/12）*36*（7/13）
=5*3*（7/13）
=（15*7）/13
=105/13

One half plus one third plus one fourth All the way up to one hundredth. Q: how do you calculate it?
It's not a problem to divide
100 is fine

The one upstairs is too exaggerated
I give Ge approximately = 4.187377517639621
1+1/2+1/3+1/4+1/5+1/6+1/7+1/8+1/9 +..+1/n>ln(n+1)
1+1/2+1/3+1/4+1/5+1/6+1/7+1/8+1/9 +..+1/n≈ln(n+1)+0.577
Ln is a natural logarithm function. You will learn it in high school

From one to half, from one to three How to use Euler's formula to calculate when it is added to one hundredth?
See this formula: 1 + 1 / 2 + 1 / 3 + 1 / 4 +... 1 / N = ln (n + 1) + R. Euler approximately calculates the value of R, which is about 0.577218, but I don't know how to substitute it into the calculation?

ln(100+1)+0.577218=5.1923385

How much is two and a half

=5/2=2.5
=（2*2+1）/2
Or = 2 + 1 / 2 = 2 + 0.5 = 2.5

How many degrees is cos equal to minus half?

COS is x / R, R is always positive, then x is negative, so it's between 90 and 270 degrees
Cos60 = 1 / 2 - X / R on Y-axis symmetry
cos120=-1/2
R can be symmetric about the X axis, and there's another angle of 240 degrees

Xiaoming's age is 5 / 6 of Xiaohua's. The Age ratio of Xiaohong to Xiaoming is 3:5. Xiaoming is 10 years old. One third of Xiaohong's age is equal to one fourth of mine
Xiaoming's age is 5 / 6 of Xiaohua's. The Age ratio of Xiaohong to Xiaoming is 3:5. Xiaoming is 10 years old. One third of Xiaohong's age is equal to one fourth of Xiaoli's. how old are Xiaohua, Xiaohong and Xiaoli?

Xiaohua: 10 △ 5 / 6 = 12
Xiaohong: 10 × 3 / 5 = 6
Xiaoli: 6 × 4 / 3 = 8

Xiao Ming read a story book. After opening it, the number of page numbers of the left and right pages added up to 121. Do you know which two pages Xiao Ming opened

(121 + 1) △ 2 = 61 (page)
121-61 = 60 (page)