suppose the fraction is x/y

if, x+1/y+1 = 4 or,y=(x-3)/4 again, x-1/y-1=7 or, y=(x+6)/7 or, (x-3)/4=(x+6)/7 or, x=15  

 suppose nominator of  the fraction is x here, x/15 =.4 or, x= 8  

30% have passed so failed =(100-30 )%=70% total failed= 21+15=36 here,  70% =36 100%=36 x 100/70 =45  

as first person have to pay 800 tk and  each of others have to pay y tk if , each of three person pays 450 tk each so, total cost = (450 x 3)= 1350 taka here, 800+2y=1350 or, 2y=550 or, y =275

1/10/3/4= 1/10 X4/3=4/30 =2/15

Value of X and Y are both tripled

XZ/Y = (3X)Z/3Y =XZ/Y

A.T.Q,

x-1/4x = 1/2

x = 2/3

Remaining = (1-2/3) = 1/3

Again,

1/3 part =100

1 part =300

2/3 part = 200

12.20-11.40=40 

40/60=2/3

(x+4)/y = x/y+2/3

Or, x/y + 4/y =  x/y + 2/3

Thus,

4/y = 2/3

Or, 2y = 12

Or, y = 12/2 = 6

সাদা= ১/৫

কালো = ১/৩

লাল = ১/১০

সুতরাং, সবুজ = ১ - ( ১/৫ + ১/৩ + ১/১০)

                  = ১ - [(৬+১০+৩) /৩০]

                  = ১ - (১৯/৩০)

                  = (৩০-১৯)/৩০

                  = ১১/৩০

এখন, তিরিশ ভাগ হিসেবে,

সাদা = ১*৬/৫*৬ = ৬/৩০

কালো= ১*১০/৩*১০ = ১০/৩০

লাল= ১*৩/১০*৩ = ৩/৩০

আর, সবুজ= ১১/৩০

দেখা যাচ্ছে যে, সবুজের অংশ সবচেয়ে বেশি।

The simplest rule of multiplication with decimal point:

1. Multiply the numbers without minding the decimal points.

2. After deriving the value,find out how many digits are there at the right side after the decimal points for every number you multiplied.

3. Place decimal point onto your derived value, equal to the sum of number of digits found in every number multiplied, counting from  from left to right.