maths
posted by joi .
The number of Samad's stamps is 30% of Derrick's stamps. The number of Derrick's stamps is 40% of Bee Hua's stamps. If they have 608 stamps, how many stamps does Derrick have?

S=.3D
D=.4B
B+D+S=608 
sorry i can't get it, pls explain further. tks

first equation, combine that with the second and third equation.
S=.3D
S=.3*.4D
Put that into the last equation.
1) B+D+.12D=608
now, solve for B in the second equation
B=D/.4=2.5D Now put that in your equation 1) above, solve for D