(1/15+3/49)*15-45/49
=1/15×15+3/49×15-45/49
=1+45/49-45/49
=1
(1/15+3/49)*15-45/49
=(1/15+3/49)×15-3/49×15
=(1/15+3/49-3/49)×15
=1/15×15
=1