Solve Mentally
40-10=
40-10=30
30-20=
30-20=10
50-10=
50-10=40
40-10=
10+30=40 so,
40-10=30
30
20, 30, 40
50-20=
50-20=30
70-30=
70-30=40
60-30=
60-30=30
30-20=
20 + 10 = 30 so,
30 - 20 = 10
41
31, 41, 51
32-20=
32-20=12
43-20=
43-20=23
75-20=
75-20=55
62-30=
30 + 32 = 62 so,
62 - 30 = 32
68
58, 68, 78
74-30=
74-30=44
89-30=
89-30=59
65-40=
65-40=25
77-40=
40 + 37 = 77 so,
77 - 40 = 37
86
76,86,96
98-40=
98-40=58
97-60=
97-60=37
81-70=
81-70=11
86-60=
60 + 26 = 86 so,
86 - 60 = 26
99
89, 99, 109