Pipe a fills a tank in 9 hours. pipe b fills
the tank in 6 hours. how long would it
take both pipes to fill the tank?

3.6 hours

Step-by-step explanation:

step 1

we know that

Pipe A fills a tank in 9 hours

so

The 100% of the tank is filled in 9 hours

using proportion

Find out what percentage of the tank is filled in 1 hour

step 2

we know that

Pipe B fills a tank in 6 hours

so

The 100% of the tank is filled in 6 hours

using proportion

Find out what percentage of the tank is filled in 1 hour

step 3

we know that

In one hour the percentage of the tank fill with both pipes is equal to

using proportion

Find out how long it takes to fill the tank 100%.