Standard penetration test (SPT) was conducted at a site. The recorded values of blow count for every 15 cm penetration at depth of 1 m are 5, 9 and 10 respectively. The water table was at the ground surface. The grain size classification showed that the size contained 40% fine sand and 60% silt. the value of SPT blow count(N) that should be used for overburden correction is ..........

1. 19