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To do well in school you'll need to master addition and subtraction with decimals.

Addition and Subtraction 3 (Difficult)

Welcome to the third quiz in our Difficult Eleven Plus maths section all about addition and subtraction. As we did in the first two quizzes, in this one we will pose you some problems involving decimal numbers.

As you will have learned, adding or subtracting decimal numbers is really no different from any adding or taking away whole numbers. The only difference is that you have another column (after the ‘units’ column). So, first add your 100s, next your 10s, then your units, and finally your decimals.

Here’s an example:

526.8 + 134.7 = (500 + 100) + (20 + 30) + (6 + 4) + (0.8 + 0.7) = 600 + 50 + 10 + 1.5 = 661.5

And now on to the quiz. Good luck!

1.
392.7 + 63.2 + 7.4 = ?
462.2
462.3
463.2
463.3
Hundreds first, then tens, units and, finally, decimals:
392.7 + 63.2 + 7.4 = (300) + (90 + 60) + (2 + 3 + 7) + (0.7 + 0.2 + 0.4) = 300 + 150 + 12 + 1.3 = 463.3
2.
82.7 + 27.3 + 309.2 = ?
417.2
418.7
419.2
420.7
Keep an eye out for decimals that add up to whole numbers: 82.7 + 27.3 is the same as 82 + 27 + 1
3.
325.8 + 18.1 + 900 = ?
1,342.9
1,324.9
1,234.9
1,243.9
You could tackle this problem starting with the highest number: 325.8 + 18.1 + 900 = (900 + 325.8) + 18.1 = 1,225.8 + 18.1 = 1,243.9
4.
0.9 + 0.3 + 1.8 = ?
2.9
3
3.1
3.2
9 + 3 + 18 = 30, so 0.9 + 0.3 + 1.8 = 3.0
Also, 0.9 + 0.2 = 1.2, then you can easily spot that 1.8 + 1.2 = 3.0
5.
436.2 - 128.4 = ?
307.8
308.2
308.8
309.2
436.2 - 128.4 = (400 - 100) + (30 - 20) + (6 - 8) + (0.2 - 0.4) = 300 + 10 + -2 + -0.2 = 310 - 2 - 0.2 = 307.8
You can treat this as a normal subtraction. Just make sure you put the decimal point in the right place. Making an estimate (the answer should be somewhere around 300) will help you avoid answers like 30.78 or 3.078!
6.
185.9 + 318.6 - 41.7 = ?
462.8
452.8
472.8
442.8
Hundreds, tens, units then decimals:
185.9 + 318.6 - 41.7 = (100 + 300) + (80 + 10 - 40) + (5 + 8 - 1) + (0.9 + 0.6 - 0.7) = 400 + 50 + 12 + 0.8 = 462.8
7.
15.3 - 97.9 + 228.2 = ?
146.5
145.6
154.6
164.5
To avoid negative numbers, you can rearrange the problem:
15.3 - 97.9 + 228.2 = 228.2 + 15.3 - 97.9 = 243.5 - 97.9 = 145.6
8.
728.6 + 60.4 - 235.4 + 100 = ?
652.6
653.2
653.6
654.2
Breaking the problem into hundreds, tens, units and decimals helps:
728.6 + 60.4 - 235.4 + 100 = (700 + 100 - 200) + (20 + 60 - 30) + (8 - 5) + (0.6 + 0.4 - 0.4) = 600 + 50 + 3 + 0.6 = 653.6
9.
16.3 - 2.4 - 16.3 + 29.1 = ?
25.5
26.7
27.6
28.3
TIP: don't waste time writing numbers that cancel each other out, e.g. 16.3 - 16.3 = 0
10.
19.8 - 21.6 + 239.4 = ?
236.7
267.3
237.6
263.7
Splitting this into hundreds, tens, units and decimal will help.
19.8 - 21.6 + 239.4 = (200) + (10 + 30 - 20) + (9 + 9 - 1) + (0.8 + 0.4 - 0.6) = 200 + 20 + 17 + 0.6 = 237.6
Author:  Frank Evans

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