We know that 172 of them were wood, so the rest are metal. To find that number we do:
276 - 172 = 104 metal pins.
To find the percentage that they were metal, take the number of metal pins and divide by the total number of pins:
104/276 is about 0.3768.
Multiply this by 100:
37.68
So, the percent of metal pins is 37.68%.
