2.4×1.25
= 2.4×1.25×4÷4
= 2.4×5÷4
= 12÷4
= 3
19-5/6-6/7-1/6
= 19 - 5/6 - 1/6 - 6/7
= 19 - 1 - 6/7
= 18 - 6/7
= 17又1/7