at

http://www.borax.com/docs/product_pdfs_data/pds-borates-potassiumpentaborate-us.pdf?sfvrsn=1

you will find potassium pentaborate solubility. since it is obtained by precipitation, you don't need to make both solutions supersatured, in precipitation saturation is related to the product of reaction, not of reagents. Let me explain: if you mix calcium chloride and sodium carbonate eve if they are diluted solutions, you will find calcium carbonate solids if the concentration allows the formation of a supersatured solution of calcium carbonate.

Thank you sir for response.

I understood what you say.

I got result