Of Ok here is what I am thinking.
Simple replacement means when one element or compound moves out of another element and is replaced by this compound.
For example if you have A+BC ----- AC + B
Most of the time the one which is replaced is found on the right and the left one is going be only one element or compound.
Double replacement means when the two compounds exchange the positive and negative ions. Ok let see this example:
AB+ CD------- AD+ BC
this means if A have + sign and D has - sign they will share to form new compound the same is true for DC. Don't forget that all compounds are formed from positive and negative ions.
QUESTIONS
CUSO4 + NA2S---- CUS + Naso4[ double replacement]
KBR +Pb[CLO3]2------K[clo3]2 +PbBr [ double replacement]
I do not think these questions can be single replacement.
I hope this may helps you.
The specific gravity of a sample is the ratio of the density of the sample with respect to one standard sample. The standard sample used in specific gravity calculation is water whose density is 1 g/mL. The solution having specific gravity 1.30 is the density of the sample that is 1.30 g/mL. Thus the weight of the 30 mL sample is (30×1.30) = 39 g.
Now the mass of the 10 mL of water is 10 g as density of water is 10 g/mL. Thus after addition the total mass of the solution is (39 + 10) = 49g and the volume is (30 + 10) = 40 mL. Thus the density of the mixture will be 
g/mL. Thus the specific gravity of the mixed sample will be 1.225 g/mL.
Iron rusts when in contact with water.
