Question

2+4+6+....+98+y=1+2+3+4+5+....+99
litera corespunzatoare raspunsului corect este
a)2.450
b)2.500
c)500
d)50
cu resolvare

Answer 1

2+4+6+...+98=
=2(1+2+3+...+49)=
=2[(49×50)÷2]=
=49×50=
=2450

1+2+3+4+...+99=
=[(99×100)÷2]=
=4950

2450+y=4950
y=2500 (b)

Answer 2

2 + 98 = 100       1 + 99 = 100

4 + 96 = 100      2 + 98 = 100

6 + 94 = 100      3 + 97 = 100

8 + 92 = 100      4 + 96 = 100

10 + 90 = 100      5 + 95 = 100

12 + 88 = 100

14 + 86 = 100

16 + 84 = 100

18 + 82 = 100

20 + 80 = 100

22 + 78 = 100

24 + 76 = 100

26 + 74 = 100

28 + 72 = 100

30 + 70 = 100

32 + 68 = 100

34 + 66 = 100

36 + 64 = 100

38 + 62 = 100

40 + 60 = 100

42 + 58 = 100

44 + 56 = 100

46 + 54 = 100

48 + 52 = 100

2400 + 50 + y = 4900

y = 2450