Hikari students to measure the density of a solid plastic ball, but found that the plastic ball placed in the water will float on the surface of the water, so Hikari design the following steps:

A. measured the quality of the plastic ball with a well adjusted balance, as shown in Figure 14a. Record the quality of plastic ball is m;

B. the amount of water poured into the cylinder as shown in Figure 14b, record the water volume is Vl;

C. with thin plastic ball hanging a small piece of iron into the water, the rest shown in Figure 14C record at cylinder shows the number of V2;

D. remove the plastic ball, the small iron alone into the water at rest as shown in Figure 14d, the number of records at this time for a V3 display;

E. uses the density formula to calculate the result.

Answer the following questions according to the experimental process.

(1) the extra steps in the experiment are: (fill in the letters).

(2) the quality of the plastic ball is measured by the balance in the experiment g p=, the density of the plastic ball kg/m3 m=. The measured value of this density is more than the real value.

(3) in the exchange Xiaohua think, ontology used equipment without balance, but also to measure the density of the plastic ball, only need to add a step in B, C, D in three steps. Please write this step.

According to your supplementary steps, write the calculation expression of rho = density of plastic ball ball. (represented by the letter, the density of water / water)