it is for math and i need help on it urgently
let me add to the already given answers
divisibility by 7: there are three steps-step 1) subtract the ones digit from the number
step 2) divide the result by 10
step 3) subtract
2 times the original ones digit from the second result
if you get a multiple of 7 (or 0, which is a multiple of all numbers), then the original number is divisible by 7
examples: is 161 divisible by 7 ?
161-1=160
160/10=16
16-2*1=16-2=14, a multiple of 7
is 126 divisible by 7 ?
126-6=120
120/10=12
12-2*6=12-12=0, a multiple of 7
is 952 divisible by 7 ?
952-2=950
950/10=95
95-2*2=95-4=91, a multiple of 7 (7*13=91)
if you did not know that 91 was a multiple of 7, simply repeat the steps with 91
91-1=90
90/10=9
9-2*1=9-2=7, obviously a multiple of 7
divisibility by 8: a number is divisible by 8 if the number formed by the three
right-most digits is divisible by 8(the number in question has to be at least 4 digits in length in order for the rule to be useful)
examples: is 1536 divisible by 8 ?
check to see if 536 is divisible by 8
536 is divisible by 8 (536/8=67)
is 502,872 divisible by 8 ?
check to see if 872 is divisible by 8
872 is divisible by 8 (872/8=109)
divisibility by 11: take the digits that form the number and subtract and then add them one at a time from left to right; if you get 0 or a multiple of 11 then the number is divisible by 11
examples: 132 1-3+2=0
13,574 1-3+5-7+4=0
75,845 7-5+8-4+5=11
also, you can make up your own divisibility rules
a number is divisible by 12 if it is divisible by both 3 and 4
a number is divisible by 14 if it is divisible by both 2 and 7
a number is divisible by 15 if it is divisible by both 3 and 5
the numbers must not have any common factors except 1 (3 and 4, 2 and 7)
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