Q9: Jenny starts a game with twice as many

October 15, 2026

2018 Test A Math · Question 9 of 57

Jenny starts a game with twice as many marbles as Keiko. Jenny gives Keiko 5 marbles, but she still has 10 more than Keiko. How many marbles did Jenny have to start with?

Show the answer

Correct answer: D

Set up some equations. Jenny (J) has twice as many marbles as Keiko (K):

$J=2K$

Jenny gives Keiko 5 marbles, so now they each have: J − 5 and K + 5 marbles. Jenny still has 10 more than Keiko:

$J-5=(k+5)+10$

To find how many marbles Jenny had to start with, solve J = 2K for K and substitute that into the second equation:

In equation J = 2K, solve for K:

$K=frac{J}{2}$

Substitute

$J-5=(K+5)+10$

$J-5=(frac{J}{2}+5)+10$

$2(J-5=(frac{J}{2}+5)+10)2$

$2J-10=J+10+20$

$2J-J=10+20+10$

$J=40$

Jenny has 40 marbles