Pre-RMO 2014/14

One morning, each member of Manjul's family drank an \(8\)- ounce mixture of coffee and milk. The amounts of coffee and milk varied from cup to cup, but were never zero. Manjul drank \(\frac{1}{7}\) -th of the total amount of milk and \(\frac{2}{17}\) -th of the total amount of coffee. How many members are there in Manjul's family?


This note is part of the set Pre-RMO 2014

#Pre-RMO

Note by Pranshu Gaba
6 years, 8 months ago

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Let the total number of members be kk, total amount of milk =x= x ounce, and total amount of coffee =y= y ounce.

We know that x7+2y17=8\dfrac{x}{7} + \dfrac{2y}{17} = 8

Therefore, 17x+14y=8×7×1717x + 14y = 8 \times 7 \times 17

Also, x+y=8kx + y = 8k

So, 3x+(14×8)k=8×7×17 3x + (14\times 8)k = 8 \times 7 \times 17

3x=56(172k)3x = 56( 17 - 2k)

x7=83(172k)\dfrac{x}{7} = \dfrac{8}{3} (17 - 2k)

It is given 0<x7<8 0 < \dfrac{x}{7} < 8

0<83(172k)<80 < \dfrac{8}{3} (17 -2k) < 8

0<172k<3 0 < 17 - 2k < 3

0>k172>320 > k - \dfrac{17}{2} > - \dfrac{3}{2}

172>k>7\dfrac{17}{2} > k > 7

7<k<8.57 < k < 8.5

The only integral value of kk satisfying this is k=8k= 8

Therefore, there are 8\boxed{8} members in Manjul's family.

Pranshu Gaba - 6 years, 8 months ago

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did the same thing..

Abhishek Bakshi - 6 years, 8 months ago

Approx 8 members

MAYYANK GARG - 6 years, 8 months ago

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We can't say apprx 8 members as that might mean there are 7.99 or 8.01 members.

Siddhesh Naik - 6 years, 7 months ago

exactly. there are apprx.5 members in my family cuz whyever not? there can be 4.8 members or even 5.3 members. Dude we are like counting members, and however dumb may maths questions get (who buys 300 watermelons, just so that kids have to calculate the total cost?) it will never make us count members in fractions. -Son of Uday Prakash (btw)

Uday Prakash - 2 years, 10 months ago
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