 See if you can do these tricky addition and subtraction problems.

In this last section of 11-plus Maths quizzes on addition and subtraction, you are going to get some practice in adding and subtracting decimals.

1. Add the whole numbers first, then add the decimal parts. For example, 1.5 + 3.6 - 2.4 = (1 + 3 - 2) + (0.5 + 0.6 - 0.4) = 2 + 0.7 = 2.7
2. With numbers less than 1,000, add the hundreds first, then the tens and then the units. For example: 120 + 360 + 25 + 8 = (100 + 300) + (20 + 60 + 20) + (5 + 8) = 400 + 100 + 13 = 513

If you don't get 10 out of 10 the first time you play the quiz, don't worry. Try it again until you have a good grasp of this important aspect of Maths. Good luck!

1.
128.7 + 450.3 - 15.2 + 200 = ?
763.9
763.7
763.8
763.6
128.7 + 450.3 - 15.2 + 200 = (100 + 400 + 200) + (20 + 50 - 10) + (8 - 5) + (0.7 + 0.3 - 0.2) = 700 + 60 + 3 + 0.8 = 763.8
2.
345.9 + 38.6 - 17.2 = ?
367.3
376.3
367.4
365.3
345.9 + 38.6 - 17.2 = (300) + (40 + 30 - 10) + (5 + 8 - 7) + (0.9 + 0.6 - 0.2) = 300 + 60 + 6 + 1.3 = 367.3
3.
0.8 + 0.2 + 0.7 = ?
1.5
1.2
0.7
1.7
0.8 + 0.2 + 0.7 = (0.8 + 0.2) + 0.7 = 1 + 0.7 = 1.7. Be on the LOOKOUT for decimals that sum to 1
4.
69.9 - 40.6 + 123.4 = ?
152.8
152.6
152.7
152.5
69.9 - 40.6 + 123.4 = (100) + (60 + 20 - 40) + (9 + 3) + (0.9 + 0.4 - 0.6) = 100 + 40 + 12 + 0.7 = 152.7
5.
200 + 158.3 + 28.9 = ?
378.2
387.2
387.1
387.0
200 + 158.3 + 28.9 = (200 + 100) + (50 + 20) + (8 + 8) + (0.3 + 0.9) = 300 + 70 + 16 + 1.2 = 387.2
6.
120.3 + 23.4 + 8.6 = ?
152.4
150.2
151.3
152.3
Add the whole numbers first, then add the decimal parts. 120.3 + 23.4 + 8.6 = (100) + (20 + 20) + (3 + 8) + (0.3 + 0.4 + 0.6) = 100 + 40 + 11 + 1.3 = 152.3
7.
678.1 - 345.2 = ?
332.8
332.7
323.9
332.9
678.1 - 345.2 = (600 - 300) + (70 - 40) + (8 - 5) + (0.1 - 0.2) = 300 + 30 + 3 - 0.1 = 333 - 0.1 = 332.9: Note: with negative numbers, the negative sign is kept with each part of the number, e.g. - 678.6 is written as -600, -70, -8, and -0.6
8.
23.5 - 14.9 + 146.2 = ?
145.8
154.8
154.7
154.6
23.5 - 14.9 + 146.2 = (100) + (20 + 40 - 10) + (3 + 6 - 4) + (0.5 + 0.2 - 0.9) = 100 + 50 + 5 - 0.2 = 154.8
9.
2.3 + 5.6 + 12.3 = ?
19.1
20.1
20.2
20.3
Add the whole numbers first, then add the decimal parts. 2.3 + 5.6 + 12. 3 = (10) + (2 + 5 + 2) + (0.3 + 0.6 + 0.3) = 10 + 9 + 1.2 = 20.2
10.
8.8 - 6.4 - 8.8 + 19.6 = ?
13.2
31.2
13.1
13.0
8.8 - 6.4 - 8.8 + 19.6 = (10) + (9 - 6) + (0.6 - 0.4) = 10 + 3 + 0.2 = 13.2: don't waste time writing numbers that cancel each other out, e.g. 8.8 - 8.8 = 0
Author:  Frank Evans