math

) A wierd number is a number that is the product of two consecutive primes, such as 7x11=77 . What is the least common multiple of the 5 smallest wierd number

7) According to an ancient belief, when a friend visits a sick person, 1/70 of his sickness is taken away. What is the least amount of friends that need to visit to take away at least 81% of a person's illness?

can any one get the answer


I don't really understand the first one.

But for the 2nd one. 1/70 = 0.01%. So 81/0.01 = 8100. Therefore, at least 8100 friends need to visit to take the illness away.

1. the first 5 'wierd' numbers are:
2x3=6
3x5=15
5x7=35
7x11=77
11x13=143

Now find the LCM of 6,15,35,77,143 which would of course be 2x3x5x7x11x13= .....

2. Raj's answer is not correct.

Look at it this way:
After the first friend 69/70 of the sickness is still there.
After the second friend visits 69/70 of the previous 69/70 of the sickness remains, or (69/70)^2 remains.

you want 81% of the sickness taken away, which means 19% remains.
So you are solving (69/70)^n = .19
an exponential equation that can be solved using logs.

I got n = log .19 / log(69/70) = 115.4

(verification: (69/70)^115 = .805...

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