Question

Mark can make $9$ pancakes in $15$ minutes, and Charlotte can make $42$ pancakes in $45$ minutes. Working together, how many minutes would it take to make $138$ pancakes?​

Answer 1

Find the time required to make $\mathbf{138}$ pancakes:

It is given that Mark can make $9$ pancakes in $15$ minutes. Also, Charlotte can make $42$ pancakes in $45$ minutes.

Mark can make $9$ pancakes in $15$ minutes.

He can make $9\times 3=27$ pancakes in $15\times 3=45$ minutes.

Also, Charlotte can make $42$ pancakes in $45$ minutes.

That means they can make $27+42=69$ pancakes together in $45$ minutes.

So that they can make $69\times 2=138$ pancakes together in $45\times 2=90$ minutes.

Therefore, Mark and Charlotte can make $\mathbf{138}$ pancakes together in $\mathbf{90}$ minutes.