Maths Problem(9)

=2+12+30+56
=100

自問自答

自問自答

自問自答

1x2+3x4+5x6+7x8
=1x2+2x2x3+2x3x5+2x2x2x7
=2(1+2x3+3x5+2x2x7)
=2[1+3(2+5)+2x2x7]
=2(1+3x7+2x2x7)
=2[1+7(3+4)]
=2(1+7x7)
=2x(1+49)
=2x50
=100
Whatever how you calculate this question
The answer should be 100 instead of 106.
Be careful that 2+12 is not equal to 20.
My method is to take the common factor, it is just a bit waste of time when doing simple question but it is really useful when you have some difficult question.
The one in the first floor gets the correct answer and the way is much more easy to follow.

2+12+30+56
=14+30+56
=44+56
=100
not
=20+30+56
=50+56
=106

1X2+3X4+5X6+7X8
=2+12+30+56
=20+30+56
=50+56
=106
所以答案係106
唔係樓上個位既100

1x2+3x4+5x6+7x8
= 2+12+30+56
= 100