3 boys and 7 girls can complete John work in 10 days . But 4 boys and 6 girls need 8 days to complete the same work . In how many days will 10 girls complete the same work?
Choose the correct choice.
A) 10 days B) 20 days C) 40 days D) 56 days E) 65 days
Work done by 4 boys and 6 girls in 1 day = 1/8   Work done by 3 boys and 7 girls in 1 day = 1/10   Let 1 man does m work in 1 day and 1 woman does w work in 1 day. The above equations can be written as   4m + 6w = 1/8 ---(1)   3m + 7w = 1/10 ---(2)   Solving equation (1) and (2) , we get m=11/400 and w=1/400   Amount of work 10 girls can do in John day = 10 × (1/400) = 1/40   Ie, 10 girls can complete the work in 40 days   40 days
<result>C</result>
3 boys and 7 girls can complete John work in 10 days . But 4 boys and 6 girls need 8 days to complete the same work . In how many days will 10 girls complete the same work?