We ignore 1/7 and 1/9 because no sum of other denominator.numbers is going to give 7ths or 9ths in the denominator
Also, 1/5 and 1/10 are not enough to add up to anything (1/10, 2/10 and 3/10 are going to leave tenths left over no matter what else you add)
What's left is 1/2, 1/3, 1/4, 1/6, 1/8.
Sum total of these is 11/8. So we need all of them except 3/8, which means 1/2+1/3+1/6.
Which is the only way to do this with egyptian fractions whose denominators are 10 or less.
Hence maximum number of Egyptian fractions needed is 3
7. If g = 10100 and H = 10g, then in which interval does g! = 1 . 2 .3 ........ 10100 lie?
Choose k, so that 10H = gλ= 10100k
k = H/100
10H = g H/100 >gg > g!
On the other hand, 10H = 10 x 10g = 10g+1 < g! (most factors are much bigger than 10)
10H < g! < 10H
10. When x + y + z = 9 and xy + yz + zx = 11, then x3 - y3 - z3 - 3xyz equals
x3Â - y3Â - z3Â - 3xyz = (x+y+z)(x2+y2+z2-xy-yz-zx) = 9[(x + y + z)2 - 3(xy + yz + zx)] = 9(81 - 33) = 432.