Page 33 - SM inner class 7.cdr

Summary

m We have learnt how to multiply two decimal numbers. While multiplying two decimal numbers, we first
multiply them as whole numbers. We then count the total number of digits to the right of the decimal point in
both the decimal numbers being multiplied. Lastly, we put the decimal point in the product by counting the
digits from its rightmost place.
m To multiply a decimal number by 10, 100, 1000 ... etc., we move the decimal point in the number to the right
by as many places as there are zeros in the numbers 10, 100, 1000 . . .etc.
m We have learnt how to divide decimal numbers.
(i) To divide a decimal number by a whole number, we first divide them as whole numbers. We then place the
decimal point in the quotient as in the decimal number.
Note that here we are con sid er ing only those di vi sions in which the re main der is zero.
(ii) To divide a decimal number by 10, 100, 1000 or any other multiple of 10, we shift the decimal point in the
decimal number to the left by as many places as there are zeros in 10, 100, 1000 etc.,
(iii) While dividing two decimal numbers, first shift the decimal point to the right by equal number of places in
both, to convert the divisor to a whole number.
m Decimal numbers which are ending with a finite number of digits in the decimal part are called terminating
decimals otherwise they called non-terminating decimals.
m A decimal in which all the digits after the decimal point are repeated is called a pare recurring decimal.
m We can convert higher unit to lower and lower to higher unit.

Review Exercise
1. Find:
(a) 7.75 ÷ 0.25 (b) 76.5 ÷ 0.15

2. The prod uct of 2 dec i mal num bers is 956.81. If one of them is 29.35 then what is the other num ber?
3. Cost of 6 pens is ` 38.10. Find the cost of 1 pen.
4. Find (a) 43.5 × 4. (b) 91.32 × 83. (c) 49.6 × 14
5. 2.35 m of cloth is needed to make a shirt. How many metre of cloth is needed to make 10 such shirts?
6. A train can run 45.8 km in one hour. What will be the dis tance trav elled by the train in 5 hours?
7. Find the value; (a) 3421.83 ÷ 3000 (b) 245.1 ÷ 30

8. With out ac tual di vi sion, de ter mine which of the fol low ing ra tio nal num bers have a ter mi nat ing dec i mal
rep re sen ta tion or non ter mi nat ing repeating decimals:
5 20 27 5 5 6 11 4 6
(a) (b) (c) (d) (e) (f) (g) (h) (i)
50 80 4 18 21 28 50 9 15

9. Con vert 175 metres to centi metres.
10. Con vert 400 metres to ki lo me ters.
2
11. Write the dec i mal form of us ing
50
(a) the place value principle (b) the long division method

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Mathematics In Focus - 7