(12 and 7 / 2-4 and 5 / 3 △ 2.3) / (10 and 7 / 2 △ 0.875)

(12 and 7 / 2-4 and 5 / 3 △ 2.3) / (10 and 7 / 2 △ 0.875)

(2 of 12 and 7-3 of 4 and 5 △ 2.3) / (2 of 10 and 7 △ 0.875)
=(2 / 12-2 / 7) / (2 / 10-0.875)
=2 / 10 and 7 / 10 × 0.875
=0.875

Simple calculation of 0.79 × 12.5

0.79×12.5
=(0.8-0.01)×12.5
=0.8×12.5-0.01×12.5
=10-0.125
=9.875

The most convenient method is to multiply 55 by 505

55 times 505 in the simplest way
55X505
=55X5X（100+1）
=275X100+275X1
=27500+275
=27775

88 times 55 is the easiest way

88*55=(8*5)*(11*11) =40*121 =4840

|21/1-20/1|+|22/1-21/21|+|23/1-22/1|+.+|30/1-29/1|
Can you answer it more clearly

∑=|21/1-20/1|+|22/1-21/1|+|23/1-22/1|+.+|30/1-29/1|
=|21-20|+|22-21|+|23-22|+…… +|30-29|
=1+1+1+…… +1
=[（30-20）*2-1]*1
=（10*2-1）*1
=19

1 / 3 + 3 / 4 + 5 / 6 + 8 / 21 + 11 / 28 + 13 / 42

1 / 3 + 3 / 4 + 5 / 6 + 8 / 21 + 11 / 28 + 13 / 42 = 1 / 3 + 3 / 4 + 5 / 6 + 8 / 21 + 11 / 28 + 13 / 42 = 4 / 12 + 9 / 12 + 10 / 12 + 8 / 3 * 1 / 7 + 11 / 4 * 1 / 7 + 13 / 6 * 1 / 7 = 23 / 12 + 1 / 7 (32 / 12 + 33 / 12 + 26 / 12) = 23 / 12 + 1 / 7 * 91 / 12 = 23 / 12 + 13 / 12 = 36 / 12 = 3

(1 / 1 + 3) + (1 / 3 + 5) + (1 / 5 + 7) + (1 / 19 + 21) = (simple calculation)

The original formula = 1 / 4 + 1 / 8 + 1 / 12 + 1 / 16 +. 1 / 40 = 1 / 4 * 1 + 1 / 4 * 1 / 2 + 1 / 4 * 1 / 3 + 1 / 4 * 1 / 4 +. 1 / 4 * 1 / 10 = 1 / 4 * (1 + 1 / 2 + 1 / 3 + 1 / 4 +. 1 / 10) this is a kind of simplification, just add 1 to 1 / 10, 1 + 1 / 2 + 1 / 3 +. 1 / N is infinite, there is no simple algorithm, of course, there are other methods for this problem, I just want to come up with

Calculation: 1 / 1 * 5 + 1 / 5 * 9 + 1 / 9 * 13 + +1/97*101
Calculation: one by five plus five by nine plus nine by thirteen, up to 97 by 101
1/1*5+1/5*9+1/9*13+…… +1/97*101

The original formula is 1 / 4 * (5-1) / 1 * 5 + 1 / 4 * (9-5) / 5 * 9 +. + 1 / 4 * (101-97) / 101 * 97
=1/4[(1-1/5)+(1/5-1/9)+...+(1/97-1/101)]
=1/4[1-(1/5-1/5)-(1/9-1/9)-...-(1/97-1/97)-1/101)]
=1/4(1-1/101)
=25/101
If you have any questions, please click [comment] or [follow up]

How to calculate 6666 * 99999 / 2222 / 33333

6666*99999÷2222÷33333
=3×99999÷33333
=3×3
=9

On the intelligence of logic
There is a cup of coffee and a cup of milk. Use a spoon to scoop a spoonful of milk from the milk cup, pour it into the coffee and stir it evenly. Then scoop a spoonful of mixed coffee and milk into the milk and stir it evenly. Now, is there more coffee in the milk cup or more milk in the coffee cup?
The answer is the same why
It's the same volume, but the back scoop is a mixture of coffee and milk

Yes, it's the same. It's hard to imagine this kind of problem. You can use a "stupid method": take a specific number. It's easy to understand
Suppose a spoonful of coffee is 10ml. A cup of coffee turns out to be 90ml (take an easy number). Then you ladle 10ml of milk into 90ml coffee. Then you ladle 10ml of mixed coffee milk back into the milk. Note that there are 9ml coffee + 1ml milk in the 10ml mixture, right? It's easy to understand. There are 9ml coffee in the milk and 9ml milk in the coffee