Question

вычислите (13/19 *3/7+13/19 *5/14+12/21*13/19 ):1/21

Answer 1

= 13/19(18/42+15/42+24/42):1/21=13/19(57/42):1/21=
=13*57*21/19*42*1=39/2=19 1/2

Answer 2

1) 13/19 * 3/7 = 39/133
2) 13/19 * 5/14 = 65/266
3) 12/21 * 13/19 = 156/399
4) 39 /133 + 65/266 = 78/266 + 65 /266 = 143/266
5) 143/266 + 156/399 = 429/798 + 312/798 = 741/798
6) 741/798 : 1/21 = 741/798 * 21= 741/38 = 19,5