Page 88 - Start Up Mathematics_8 (Non CCE)

Thinking Skills

Tick the correct answer
Between which of the following pairs of numbers does the:
1. Cube root of –72 lie?
(a) Between –3.9 and –3.8 (b) Between –4.0 and –3.9
(c) Between –4.1 and –4.0 (d) Between –4.2 and –4.1
2. Cube root of 20 lie?
(a) Between 2.5 and 2.6 (b) Between 2.6 and 2.7
(c) Between 2.7 and 2.8 (d) Between 2.8 and 2.9
(Hint: Refer cube root tables)
TABLE OF CUBE ROOTS

Number Cube Root Number Cube Root Number Cube Root
1 1.000000 26 2.962496 51 3.708433
2 1.259921 27 3.000000 52 3.732511
3 1.442250 28 3.036589 53 3.756286
4 1.537401 29 3.072317 54 3.779763
5 1.709976 30 3.107232 55 3.802952
6 1.817121 31 3.141331 56 3.825862
7 1.912931 32 3.174802 57 3.848501
8 2.000300 33 3.207534 58 3.870877
9 2.080084 34 3.239612 59 3.892996
10 2.154435 35 3.271066 60 3.914868
11 2.223930 36 3.301927 61 3.936497
12 2.239429 37 3.332222 62 3.957891
13 2.351335 38 3.361975 63 3.979057
14 2.410142 39 3.391211 64 4.000000
15 2.466212 40 3.419952 65 4.029726
16 2.519842 41 3.448217 66 4.041240
17 2.571282 42 3.476027 67 4.061548
18 2.620741 43 3.503398 68 4.081655
19 2.663402 44 3.533348 69 4.101566
20 2.714418 45 3.556893 70 4.121285
21 2.758924 46 3.583047 71 4.140818
22 2.802039 47 3.608826 72 4.160168
23 2.843367 48 3.634241 73 4.179339
24 2.884499 49 3.659305 74 4.193336
25 2.924018 50 3.684031 75 4.217163

Some NCERT Textbook Questions

1. Find the smallest number by which each of the following numbers must be multiplied to obtain a perfect
cube.
(i) 243 (ii) 256 (iii) 72 (iv) 675 (v) 100
2. Find the smallest number by which each of the following numbers must be divided to obtain a perfect
cube.
(i) 81 (ii) 128 (iii) 135 (iv) 192 (v) 704
3. State true of false.
(i) Cube of any odd number is even.
(ii) A perfect cube does not end with two zeros.
(iii) If square of a number ends with 5, then its cube ends with 25.
(iv) There is no perfect cube which ends with 8.
(v) The cube of a two digit number may be a three digit number.

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