Answer:
Let's calculate the total number of blocks Ed has after throwing out the broken ones and adding the two packs of blocks:
Initial number of blocks: 147
Broken blocks: -28
Blocks from cousin: +2 x 48 = 96
Total blocks: 147 - 28 + 96 = 215
So Ed actually has 215 blocks, which is quite a bit less than his estimate of 300. Therefore, his estimate is not very good.