Problem
The tens digit must be 2 or 3, so the only candidates that can be closest to 30 are 27.xx and 32.xx.
Reading the tens place tells you the rough size, just like ordering whole numbers.
5.NBT.A.1Make A Systematic ListWith 2 and 7 as the whole part, the closest is 27.43; with 3 and 2, the closest is 32.47.
Pick the digit arrangement that nudges each candidate toward 30.
4.NF.C.7Guess And Check30 - 27.43 = 2.57 and 32.47 - 30 = 2.47, so 32.47 is nearer to 30.
The smaller the difference, the closer the number - so compute both gaps and pick the smaller.
5.NBT.B.7Guess And CheckThe candidate closer to 30 is the one whose gap to 30 is smaller, so comparing the two gaps decides which number wins.
Closeness to 30 is just how far a number sits from 30, so the candidate with the shorter distance is the nearer one.
The distance to 30 is found by subtracting: it is the amount you must add to the candidate to reach 30, or take off to come back down.
The two gaps 2.57 and 2.47 have the same whole part 2, so the tenths place decides it, and 4 tenths is less than 5 tenths.
When the larger places match, the next place down settles the size, because each place is worth ten of the place to its right.
Closest to 30 means smallest gap - so just check the numbers right below and right above 30 and subtract!