Question

George needs to calculate the following sum as quickly as possible:


The quickest approach is .

• A. (2.2 + 5.3) + 7.8
• B. (2.2 + 7.8) + 5.3
• C. (7.8 + 5.3) + 2.2

Answer 1

The correct option is B (2.2 + 7.8) + 5.3

The decimals in the given calculation can be broken down as:
2.2 = 2 + 0.2
5.3 = 5 + 0.3
7.8 = 7 + 0.8

Hence, the sum 2.2 + 5.3 + 7.8 can be expressed as:
2.2 + 5.3 + 7.8 = 2 + 0.2 + 5 + 0.3
+ 7 + 0.8

Now, calculating the result of 0.2 + 0.8 by place value table, we get:


So, 0.2 + 0.8 = 1.0

Hence, grouping the decimals with the numbers 2 and 8 in their tenths place together make the calculation more simpler.

∴ Using the associative property, the quickest approach to calculate 2.2 + 5.3 + 7.8 can be expressed as (2.2 + 7.8) + 5.3.


So, George will do the calculation as:
(2.2 + 7.8) + 5.3