Пошаговое объяснение:

№1

1) 6. 1/8 + 2. 2/5 = 6. 5/40 + 2. 16/40 = 8. 21/40

2) 2. 1/5 : 8. 21/40 = 11/5 : 341/40 = 11/5 * 40/341 = 1/1 * 8/31 = 8/31

3) 6,27 *0,01 = 627/100 * 1/100 = 627/10000

4) 4. 1/8 * 2 = 33/8 * 2 = 66/8 = 8. 2/8 = 8. 1/4

5) 8/31 + 627/10000 + 8. 1/4 = (8/31 + 8. 1/4) + 627/10000 = (32/124 + 8. 31/124) + 627/10000 = 8. 63/124 + 627/10000 = 8. 157500/310000 + 19437/310000 = 8. 176937/310000

№2

4,5 : х = 0,62 : 1. 1/4

4,5 : х = 0,62 : 1,25

0,62 * х = 1,25 * 4,5

0,62х = 5,625

х = 5,625 : 0,62

х = 5625/1000 : 62/100

х = 5625/1000 * 100/62

х = 5625/10 * 1/62

х = 5625/620

х = 9. 45/620

х = 9. 9/124

№3

3,2х + 1. 1/4х + 5,2 = 21. 1/2

3,2х + 1,25х + 5,2 = 21,5

3,2х + 1,25х = 21,5 - 5,2

4,45х = 16,3

х = 16,3 : 4,45

х = 163/10 : 445/100

х = 163/10 * 100/445

х = 163/1 * 10/445

х = 1630/445

х = 3. 295/445

х = 3. 59/89

№4

С = 7,2π см

S = ? см²

С = 2πR

R = C/2π

R = 7,2π/2π = 3,6 см

S = πR²

S = π * 3,6² = π * 12,96 = 12,96π см²