51 * 101 simple calculation =（50+1）*（100+1） =50*100+50+100+1 =5000+50+100+1 =5151 Is that right? I can't understand one movie. Why should I add one to 50 * 100 + 50 + 100 + 1?

51 * 101 simple calculation =（50+1）*（100+1） =50*100+50+100+1 =5000+50+100+1 =5151 Is that right? I can't understand one movie. Why should I add one to 50 * 100 + 50 + 100 + 1?

If you open the brackets, it is (50 + 1) x (100 + 1) = 50x100 + 50x1 + 100x1 + 1x1
=5000+50+100+1

7 / 8 * 5 / 6 ﹣ 5 / 8 24 ﹣ 0.4 ﹣ 2 / 3 2 / 15 * 3 / 4 + 2 / 3 ﹣ 4 / 3 (2 / 17 + 1 / 3) ﹣ 5 / 51 the simple calculation is 4 / 9x = 2 / 3 1 / 2x + 1 / 5x = 14
11/12-3x=1/4 2/3+2x=4/5

7/8*5/6÷5/8
=7/8*5/6*8/5
=7/8*4/3
=7/6
24÷0.4÷2/3
=60÷2/3
=60*3/2
=902
2/15*3/4+2/3÷4/3
=2/15*3/4+2/3*3/4
=(2/15+2/3)*3/4
=4/5*3/4
=3/5
（2/17+1/3）÷5/51
=(2/17+1/3)*51/5
=2/17*51/5+1/3*51/5
=6/5+17/5
=23/5
4/9x=2/3
x=2/3÷4/9
x=2/3*9/4
x=3/2
1/2x+1/5x=14
(1/2+1/5)x=14
7/10x=14
x=14+7/10
x=14*10/7
x=20

Find the law What's the number in 1997

The solution is as follows,
Find the rules first
1997 = 1 + 1 + 2 + 3 + 4 + 5 + +1995+1996=1+（1+1996）*1996/2=1993007

A series of numbers 1, 2, 4, 7, 11, 16, 22, 29... The composition rule of this series of numbers is that the second number is 1 more than the first number, and the third number is 2 more than the second number,
And so on, what is the remainder of the number from the left of this column divided by 5

The general term of sequence is an = n * (n-1) / 2 + 1
A1992=1992*1991/2+1=1983037
Divided by five, the remainder is two