p and q can complete a work in 20 days and 12 days respectively . p alone started the work and q joined him after 4 days till the completion of the work . how long did the work last ?
"explanation : work done by p in 1 day = 1 / 20 work done by q in 1 day = 1 / 12 work done by p in 4 days = 4 × ( 1 / 20 ) = 1 / 5 remaining work = 1 – 1 / 5 = 4 / 5 work done by p and q in 1 day = 1 / 20 + 1 / 12 = 8 / 60 = 2 / 15 number of days p and q take to complete the remaining work = ( 4 / 5 ) / ( 2 / 15 ) = 6 total days = 4 + 6 = 10 answer : option b"
add(4, divide(subtract(const_1, divide(4, 20)), add(inverse(20), inverse(12))))