Question

A and B do work in 15 days B and C do it in 20 days if B can do it in 60 days how long can A and C do it together?

Answer 1

(A + B)'s 1 day work = \(\frac{1}{15}\)

(B + C)'s 1 day work = \(\frac{1}{20}\)

B alone 1 day work = \(\frac{1}{60}\)

Add all:

(A + 2B + C)'s 1 day work = \(\frac{1}{15} + \frac{1}{20} + \frac{1}{60}\)

Now subtract B's 1 day work:

(A + 2B + C - 2B)'s 1 day work = \(\frac{1}{15} + \frac{1}{20} + \frac{1}{60} - \frac{2}{60}\)
Solving it we get:

(A + C )'s 1 day work = \(\frac{1}{10}\)

So, (A + C) both will finish in 10 days..

Answer 2

oh great thanx that makes sense. :)

Answer 3

(A + 2B + C)'s 1 day work = 1/15+1/20 NOT '1/15+1/20+1/60'

Answer 4

wait there's choices
A) 15 days
B) 17 days
C) 16 days
D) 18 days
E) 12 days

Answer 5

Wait I have done it wrong..
There is one more method..

Answer 6

yeah i think u need to take it slow

Answer 7

The answer is 'E'

Answer 8

so after adding A and C wat dyu do nxt to get 12 days?

Answer 9

(A + B)'s 1 day work = \(\frac{1}{15}\)

So subtract B's 1 day work form it:

A's 1 day work =
\[\frac{1}{15} - \frac{1}{60} = \frac{3}{60}\]

Similarly,

(B + C)'s 1 day work = \(\frac{1}{20}\)

Subtract B's 1 day work here:

C's 1 day work =
\[\frac{1}{20} - \frac{1}{60} = \frac{2}{60}\]

Now add both:
(A + C)'s 1 day work: \(\frac{3}{60} + \frac{2}{60} = \frac{5}{60} = frac{1}{12}\)

(A + C)'s will complete in 12 days..

Answer 10

(A + C)'s 1 day work:
\[\frac{3}{60} + \frac{2}{60} = \frac{5}{60} = \frac{1}{12}\]

So, (A+C)'s will complete it in 12 days..

Answer 11

just like what waterineyes wrote

Answer 12

right i think im startin to get it now