Given: #7.351#

Just for demonstration I am going to insert the part of the number we are interested in inside square brackets.

Write #7.351" as "[color(white)(2/2)7.3]51#

The number immediately to the right of the closing bracket is 5.

The general rule is:

#color(brown)("If the trailing number ( my choice of wording) is 5 or more then we")#

#color(brown)("round up. If the 'trailing number' is less than 5 we round down.")#

#color(brown)("By 'rounding down' they mean that the number part inside the")#

#color(brown)("brackets is left as it is and the number part outside is discarded")#

#" "5>=5" so round up"#

#" "bar(ul(|color(white)(2/2) "So "7.351 =7.4" to 1 decimal place"color(white)(2/2|))| )#

'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Just to make the process clearer

Suppose we had #[color(white)(2/2)7.3]21#

#2<5# so we round down giving #7.3#

Suppose we had #[color(white)(2/2)7.3]61#

#6>5# so we round up giving #7.4#