Starting zeros are not significant and so the number of significant digits starts from 24561. The 3 digits lands on 5 but the digit next to it is more than 5(6) and so 1 is added to the 5 to make it 6. NOTE Zeros between other digits are significant. Only starting zeros are insignificant. For instance 3.052306, all the zeros are significant because they are not starting zeros after a decimal point.