Allowable operations:
Addition, subtraction, multiplication, division
Parentheses
Concatenation (77 or 777, for example)
Exponentiation (7^7, for example)
Square root (sqrt(7), for example)
Decimal (.7 = 7/10)
Repeating decimal (.7 with a line over the 7 = 7/9)
Factorials (7! = 7*6*5*4*3*2*1)
2007-01-01 02:13:13 · 6 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
77 uses two 7s. For example, 77/7 gives an end result of 11 using three 7s.
Counting to 5:
1 = 7^(7 - 7)
2 = (7 + 7) / 7
3 = (7 / .7) - 7
4 = ????
5 = 7 / (.7 + .7)
2007-01-01 02:52:47 · update #1
A bit complicated but allowed:
sqrt(7+7/repeating decimal(7)) = sqrt(7+9) = 4
2007-01-01 07:12:25 · answer #1 · answered by chaps 2 · 0⤊ 0⤋
I can do it with five 7s:
[77 - (7x7)] / 7 = (77 - 49) / 7 = 28 / 7 = 4
or (7 + 7 + 7 + 7)/ 7 = 28 / 7 = 4
I can do it with four 7s:
(77/7) - 7 = 11 - 7 = 4
or 7 - [(7/.7) - 7] = 7 - (10 - 7) = 7 - 3 = 4
or (7 + 7) - (7/.7) = 14 - 10 = 4
or mod (7) (77/7) = 4
But the nearest I can get with three 7s is a bit of a cheat. I need the sign for "plus or minus" which I shall write as p/m and I need to represent ,7 recurring and will write that as .7r
7 p/m sqrt (7/.7r)
The cheat involves dealing with the negative square root (-3) by adding it and dealing with the positive square root (+3) by subtracting it but a more rigorous solution eludes me for now.
If the floor command is allowed, you can do this several ways with just two sevens:
floor (7 - sqrt 7)
or floor (sqrt 7) x floor (sqrt 7)
or floor (sqrt 7) + floor (sqrt 7)
or floor (sqrt 7) ^ floor (sqrt 7)
2007-01-01 11:15:51 · answer #2 · answered by brucebirchall 7 · 0⤊ 0⤋
1. Concatenate 77
2. Divide by 7 11
3. Subtract 7 4
2007-01-01 10:38:09 · answer #3 · answered by teacher2006 3 · 0⤊ 0⤋
7+7+7=? ( mod17)
answer: 4
2007-01-01 11:20:07 · answer #4 · answered by iyiogrenci 6 · 0⤊ 0⤋
just sevens or other numbers too?
7x3 = 21+7=28/7=4
2007-01-01 10:23:16 · answer #5 · answered by strkrs4 2 · 0⤊ 0⤋
I can do it with two 7s and the floor function floor(7*.7) hmmmmm
2007-01-01 11:15:18 · answer #6 · answered by a_math_guy 5 · 0⤊ 0⤋