9+9=90

số liền sau số 42 la 43

43+16=58

58-23=35

vay so do la 35

a

2

vi 1+4=5

2+5=7:tong 1+4+2+5=12

tuong tu 1+4+2+5+3+6=21

vay ?=1+4+2+5+3+6+8+11=40

a,thung thu nhat co so l dau la:

45+8=53(l)

b,thung thu hai co so l dau la:

45-8=7(l)

       DS:

C.9

so lien sau 64 la 65

so can tim la

65-24=41