This is Simple, Just Subtract Time taken by Science homework from time taken by Maths homework..

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1. {2x−3y=9
{3x+5y=4
2. {(2x−3y=9)×5
{(3x+5y=4)x3
3. {10x-15y=45
{9x+15y=12
4. (10x-15y=45) + (9x+15y=12)= (19x=57)
5. (19x=57)÷19
6. x=3
7. 2(3)-3y=9
8. 6-3y=9
9. -3y=9-6
10. (-3y=3)÷(-3)
11. y=-1
Answer: x=3 and y=-1
Answer:
Total number of cards in a standard deck of card=52
As deck of card contain 13 club +13 heart +13 spade+13 Diamond.
P(Diamond)=13/52 =1/4
If the card is not diamond then
P(not diamond)=39/52=3/4
Since after drawing card is not replaced
P ( second Diamond)=12/51
now if second card is not Diamond.then
P(non diamond)=39/51
Chances of your winning i.e both cards are diamonds=1/4×12/51=1/17=0.0588..(approx)
chances of your friend winning=1/4×39/51=[1/4]×[13/17]=13/68=0.1911..(approx)
Your friend has got better chance to win because there are more chances that both the cards are not Diamonds.