Page 20 - SM inner class 6.cdr

Double the last digit, then subtract result 357:
from the rest of the digits.
double of 7 = 14
7 Repeat for larger numbers until result is a
2-digit number then check if subtract 14 from 35 = 21
21 = 3 ´ 7
2 digit is divisible by 7 or not divisible by 7
1. Hundred’s digit even : last 2 digits 986,104:
divisible by 8
1. hundreds digit = 1, odd
8 Hundred’s digit odd: add 4 to last 2 digits
and sum divisible by 8 04 4+ = 8
2. Last 3 digits = 104 Þ 104 = 13 8
´
2. Last 3 digits divisible by 8
Add all the digits in the number. 24,343,785:
+
+
+
+
+
9 Repeat until sum is 2-digits. 2 4 3 4 3 7 8 5 = 36
+
+
2-digits divisible by 9. 36 = 4 ´ 9
34,789,013,467,593,487,540:
10 Last digit is 0
Last digit = 0
918,082:
1. Alternatively subtract then add the digits
´
11 from L to R; result divisible by 11 1. 9 1 8 0 8 2- + - + - = 22 Þ 22 = 2 11.2
627;
2. Subtract last digit from the rest
´
2. 627 62: - 7 = 55 Þ 55 = 5 11
324: 3 2 4+ + = 9, divisible by 3,
12 Divisible by 3 and 4
24 divisible by 4
,
)
´
13 Iteratively add 4 times the last digit to the rest 637: 63+ ( 7 4 = 91 Þ 7 13
´
E xercise 3.2
1. Sepa rate the follow ing into even and odd numbers with out carry ing divi sion.
(i) 6423 (ii) 8321 (iii) 6254 (iv) 989
(v) 810 (vi) 8394 (vii) 1234 (viii) 1357
(ix) 54321 (x) 86420 (xi) 99880 (xii) 30005
2. Which of the follow ing numbers are divis i ble by 3, by 4, by 5, by 6, by 7 and by 10.
(i) 762 (ii) 512 (iii) 110 (iv) 968
(v) 3692 (vi) 5361 (vii) 1215 (viii) 7310
(ix) 1010 (x) 12345
3. Using the divisibility tests, deter mine which of the follow ing numbers are divis i ble by 8 or 9.
(i) 512 (ii) 333 (iii) 440 (iv) 904
(v) 56565 (vi) 2968 (vii) 6669 (viii) 11241
(ix) 16920 (x) 11088
4. Find the number which is divis i ble by 11.
(i) 2550 (ii) 3673 (iii) 8415 (iv) 5155
(v) 135795 (vi) 21211212 (vii) 7654321 (viii) 654313
5. Which of the follow ing numbers are divis i ble by 12 or 13.
(i) 312 (ii) 576 (iii) 729 (iv) 1140
(v) 1335 (vi) 4428 (vii) 3150 (viii) 612
(ix) 11112 (x) 12345

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Mathematics In Focus - 6