Please select seven of the 45 unit fractions, one-half, one-third, one-quarter, one-fifth and one-forty-six, and add a plus or minus sign to make their sum equal to 1,

Please select seven of the 45 unit fractions, one-half, one-third, one-quarter, one-fifth and one-forty-six, and add a plus or minus sign to make their sum equal to 1,

1 / 2 + 1 / 3 + 1 / 4 - 1 / 12 + 1 / 5 - 1 / 6 - 1 / 30 = 1

Let's solve the following math problem!
Acrobats perform unicycle walking steel wire, the diameter of the wheel is 40 cm, to ride 21.4 meters long steel wire, the wheel to rotate how many cycles?
The minute hand of a wall clock is 20 cm long. After 45 minutes, how many cm does the tip of the minute hand travel?
Let's help. Cheering!

Acrobats perform unicycle walking steel wire, the diameter of the wheel is 40 cm, to ride 21.4 meters long steel wire, the wheel to rotate how many cycles?
Of course, if the wheels don't slip
Wheel circumference = diameter x π = 40 * 3.14
Number of turns = 21.4 / (40 * 3.14) = you should be able to calculate by yourself
The minute hand of a wall clock is 20 cm long. After 45 minutes, how many cm does the tip of the minute hand travel?
If the tip of the minute hand goes one circle, the circumference drawn is 2 * 20 * π. Now it's 45 minutes. This minute hand has gone 3 / 4 circles, so it's = 2 * 20 * 3.14 * 3 / 4

Many 15 cm long short ropes are used to join a long rope. Each knot needs 1 cm for each short rope. At least how many short ropes can be used to join a long rope no less than 5 meters?
1992 2
——After subtracting a number from the numerator and adding this number to the denominator, the fractional value is - what is the number?
1993 3

According to the meaning of the question: 15x - (x-1) × 2 ≥ 50015x-2x-2 ≥ 50013x ≥ 502x ≥ 502 △ 13X ≥ 38.615384615384615384615384615385 because x is an integer, so the minimum is 39 (1992-a) / (1993 + a) = 2 / 32 (1993 + a) = 3 (1992-a) 3986 + 2A = 59