One tenth is 10 hundredths, so 3 tenths are 30 hundredths, and with the 7 hundredths already there that is 37. Adding the two counts instead gives 10, which merges two different places into one.
Question 2
Which is the greatest, 29 hundredths, 3 tenths or 9 thousandths?
(a)29 hundredths
(b)9 thousandths
(c)3 tenths
Show answer
(c) 3 tenths
3 tenths. Written as decimals, 29 hundredths is 0.29, 3 tenths is 0.3 and 9 thousandths is 0.009. The tenths place decides: 0.3 has the most tenths, so 3 tenths is the greatest. Naming a smaller place never makes a part bigger.
Splitting a unit into ten equal parts
Question 3
One leaf measures 81 tenths of a unit and another 36 tenths. What is the difference, in whole units and tenths?
(a)
(b)
(c)45
Show answer
(a)
The counts differ by 45 tenths. Every ten tenths make one whole unit, so the difference is . The answer 45 treats tenths as whole units.
Question 4
A sequence goes , , , ... What is the next term?
(a)
(b)
(c)
Show answer
(b)
Each term is more than the one before. Adding that step takes the tenths to 18. Ten tenths make one whole unit, so the term is . Leaving the tenths at 18 gives .
Adding and subtracting decimals by place
Question 5
What is 12.6 - 9.09?
(a)3.69
(b)3.51
(c)21.69
Show answer
(b) 3.51
12.6 has no hundredths of its own, so one tenth is borrowed and arrives as ten of them: 3.51. Bringing the 9 hundredths straight down instead of subtracting it gives 3.69 -- which is more than 3.51, though something has just been taken away.
Question 6
Someone worked out 0.934 + 0.6 and wrote 0.940. What went wrong?
(a)Nothing went wrong; the columns line up.
(b)The carry out of the tenths was forgotten.
(c)The columns were lined up from the right instead of by place.
Show answer
(c) The columns were lined up from the right instead of by place.
The columns were lined up from the right instead of by place. 0.6 was pushed right until its last digit sat under the last digit of 0.934, so its 6 was counted as 6 thousandths instead of 6 tenths. The right answer is 1.534, and nothing here is a carrying mistake: the columns themselves were wrong.
When a zero changes the value and when it does not
Question 7
Which of these numbers is equal to 0.2?
(a)0.02
(b)2
(c)0.20
Show answer
(c) 0.20
0.20. A zero written at the end says there are no hundredths, which was already true, so nothing changes. In 0.02 the zero pushes the 2 into a smaller place, making it a tenth of what it was. 2 is a whole number, but in 0.2 the 2 counts tenths.
Question 8
Compare 13.8 and 13.800 place by place. Which one is greater, or are they equal?
(a)13.8
(b)They are equal
(c)13.800
Show answer
(b) They are equal
They are equal: 13.800 is 13.8 with two zeros written on the end, and a zero at the end adds no parts. The longer form has more digits but not more quantity -- every place they both have holds the same digit.
Writing a plain count of tenths or hundredths in decimal form
Question 9
Write in decimal form.
(a)1.2
(b)0.12
(c)12
Show answer
(a) 1.2
The number below the line says which place the digits end in: tenths end one place after the point, so is 1.2. 12 is what the next place up would give, and 0.12 what the next place down would give.
Question 10
How many tenths make 23.4?
(a)2340
(b)234
(c)4
Show answer
(b) 234
Each whole unit is 10 tenths, so 23 units are 230 tenths, and with the 4 already after the point that is 234. The tenths are not only what stands after the point -- that would be 4 -- and 2340 is the count of HUNDREDTHS.
Placing decimals on a number line and comparing them
Question 11
A number line runs from 1 to 1.1, divided into ten equal parts. What decimal number does the fourth division after 1 stand for?
(a)1.4
(b)1.04
(c)5
Show answer
(b) 1.04
The ten divisions share one tenth, so one division is 0.01, and the mark stands four divisions along: 1.04. Calling every division a tenth gives 1.4, and counting the divisions as whole units gives 5.
Question 12
The number line runs from 4.18 to 4.19 and is divided into ten equal parts. What is the value of one division?
(a)0.1
(b)0.001
(c)0.0001
Show answer
(b) 0.001
The line spans one hundredth, and ten divisions share it, so each one is 0.001. A division is only a tenth when the line spans exactly one unit; here 0.1 would make the line span 1 unit instead.
Converting between units with a decimal point
Question 13
A toll booth collects 20 paise per vehicle as a levy from 15,000 vehicles. What is the total?
(a)₹30,000
(b)₹3,00,000
(c)₹3,000
Show answer
(c) ₹3,000
Each charge is 20 paise, which is ₹0.20, and there are 15,000 of them: ₹3,000. Reading the paise as tenths of a rupee makes each charge ₹2 and the total ₹30,000, ten times too much, while ₹3,00,000 leaves the paise counted as whole rupees.
Numbers written with a point that are not decimals
Question 14
3 m 8 mm is to be written in meters using a decimal point. What decimal number should it be written as?
(a)3.8 m
(b)3.08 m
(c)3.008 m
Show answer
(c) 3.008 m
1000 mm make 1 m, so 8 mm is 8 thousandths of a meter. Thousandths sit in the third place after the point, so the tenths place and the hundredths place are empty and each holds a zero. That gives 3.008 m. Putting the smaller unit's count straight after the point gives 3.8 m, which is a far bigger quantity.
The decimal point and the places on either side of it
Question 15
Which is bigger, 7.05 or 7.5?
(a)7.05
(b)They are the same quantity
(c)7.5
Show answer
(c) 7.5
7.5. They are not the same quantity: the zero in 7.05 holds the tenths place, so its 5 is worth 5 hundredths where the other number's is worth 5 tenths -- ten times more.
0.35 is greater than 0.4 because 35 is greater than 4.
Why it feels right. I compare the digits after the point as whole numbers.
Right
Compare tenths with tenths and hundredths with hundredths.
Worked example
0.35 · 35 squares
0.4 = 0.40 · 40 squares
Both grids have 100 equal squares. The grid for 0.40 has five more shaded squares than the grid for 0.35.
Write 0.4 as 0.40.
On a hundred-square, 40 squares cover more than 35 squares.
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