№1.
3/7 : 1/2 = 3/7 × 2/1 = 6/7
1 2/5 : 2 3/5 = 7/5 : 13/5 = 7/5 × 5/13 = 7/13
№2.
3/7 × х = 5
х = 5 : 3/7 = 5/1 × 7/3 = 35/3
х= 11 2/3
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3/7 × 11 2/3 = 5
3/7 × 35/3 = 5
35/7 = 5
5=5
№3.
(3/8 + (1/2)² + 1 1/4) : 5/3 =
= (3/8 + 1/4 + 1 1/4 ) × 3/5 =
= (3/8 + 2/8 + 1 2/8 ) × 3/5 =
= 1 7/8 × 3/5 = 15/8 × 3/5 =
= 9/8 = 1 1/8
№4.
Числитель:
3,5 × 2,1 : 0,7 -2,5= 7,35:0,7 - 2,5= 10,5 - 2,5=8
Знаменатель:
16 × 3/4 - 4 = 16/1 × 3/4 - 4 = (4×3)/(1×1) - 4 = 12 -4 = 8
№5.
(3,7 - 2,2)/х + 2х = 1,5/х + 2х
при х = 1,5
1,5/1,5 + 2*1,5 = 1 + 3 = 4
при х= 3
1,5/3 + 2*3 = 0,5 +6 = 6,5